diff --git a/src/Controller/Admin/AccommodationBooking/ChangeAccommodationController.php b/src/Controller/Admin/AccommodationBooking/ChangeAccommodationController.php
index 73d3d021..205b44b7 100644
--- a/src/Controller/Admin/AccommodationBooking/ChangeAccommodationController.php
+++ b/src/Controller/Admin/AccommodationBooking/ChangeAccommodationController.php
@@ -6,11 +6,13 @@ namespace App\Controller\Admin\AccommodationBooking;
 
 use App\Entity\Groups\Accommodation;
 use App\Entity\Groups\AccommodationBooking;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Admin\Groups\AccommodationBookingChangeAccommodationType;
 use App\Htmx\HxTrait;
 use App\Service\AccommodationBookingService;
 use Psr\Log\LoggerInterface;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\Form\FormError;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Attribute\Route;
@@ -49,7 +51,24 @@ class ChangeAccommodationController extends AbstractController
             $selected = $form->get('accommodation')->getData();
 
             if ($selected instanceof Accommodation && $selected !== $booking->getAccommodation()) {
-                $this->bookingService->changeAccommodation($booking, $selected);
+                try {
+                    $this->bookingService->changeAccommodation($booking, $selected);
+                } catch (ImplausibleBookingPriceException $e) {
+                    // The house that was picked prices this stay implausibly high, so the change
+                    // did not happen. Reported in the modal the office is standing in front of —
+                    // the same treatment the create and edit forms give it.
+                    $this->logger->error('Refused to change accommodation over an implausible booking total', [
+                        'exception' => $e,
+                        'id' => $booking->getId(),
+                        'accommodation' => $selected->getCalendarCode(),
+                    ]);
+                    $form->addError(new FormError(ImplausibleBookingPriceException::FORM_ERROR_MESSAGE));
+
+                    return $this->render('admin/accommodation_booking/modal_change_accommodation.html.twig', [
+                        'booking' => $booking,
+                        'form' => $form,
+                    ]);
+                }
 
                 $this->addFlash('success', 'Das Gruppenhaus wurde geändert. Bitte wähle die Leistungen neu aus.');
 
diff --git a/src/Controller/Admin/AccommodationBooking/CreateController.php b/src/Controller/Admin/AccommodationBooking/CreateController.php
index b38b9e0e..ee4483bf 100644
--- a/src/Controller/Admin/AccommodationBooking/CreateController.php
+++ b/src/Controller/Admin/AccommodationBooking/CreateController.php
@@ -6,12 +6,15 @@ namespace App\Controller\Admin\AccommodationBooking;
 
 use App\Entity\Groups\AccommodationBooking;
 use App\Entity\User;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Admin\Groups\AccommodationBookingCreateType;
 use App\Htmx\HxRedirectResponse;
 use App\Service\AccommodationBookingService;
 use Doctrine\ORM\EntityManagerInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\Form\FormError;
+use Symfony\Component\Form\FormInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Attribute\Route;
@@ -45,8 +48,7 @@ class CreateController extends AbstractController
         ]);
         $form->handleRequest($request);
 
-        if ($form->isSubmitted() && $form->isValid()) {
-            $this->bookingService->refreshPriceSnapshot($booking);
+        if ($form->isSubmitted() && $form->isValid() && $this->refreshPriceSnapshot($form, $booking)) {
             $this->entityManager->persist($booking);
             $this->entityManager->flush();
 
@@ -65,4 +67,31 @@ class CreateController extends AbstractController
             'form' => $form,
         ]);
     }
+
+    /**
+     * The price is computed after validation, so an implausible total cannot be a constraint on
+     * the form — it is reported as one anyway, because the office's next move is to go and fix
+     * the house's prices, not to read an error page.
+     *
+     * @param FormInterface<AccommodationBooking> $form
+     */
+    private function refreshPriceSnapshot(FormInterface $form, AccommodationBooking $booking): bool
+    {
+        try {
+            $this->bookingService->refreshPriceSnapshot($booking);
+
+            return true;
+        } catch (ImplausibleBookingPriceException $e) {
+            $this->logger->error('Refused to store an implausible accommodation booking total', [
+                'exception' => $e,
+                'id' => $booking->getId(),
+                'accommodation' => $booking->getAccommodation()?->getCalendarCode(),
+                'paxCount' => $booking->getPaxCount(),
+                'nights' => $booking->getNights(),
+            ]);
+            $form->addError(new FormError(ImplausibleBookingPriceException::FORM_ERROR_MESSAGE));
+
+            return false;
+        }
+    }
 }
diff --git a/src/Controller/Admin/AccommodationBooking/EditController.php b/src/Controller/Admin/AccommodationBooking/EditController.php
index 85a495a4..bb73e028 100644
--- a/src/Controller/Admin/AccommodationBooking/EditController.php
+++ b/src/Controller/Admin/AccommodationBooking/EditController.php
@@ -7,6 +7,7 @@ namespace App\Controller\Admin\AccommodationBooking;
 use App\Entity\Groups\AccommodationBooking;
 use App\Entity\Groups\AdditionalService;
 use App\Entity\Groups\BoardService;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Admin\Groups\AccommodationBookingType;
 use App\Repository\Groups\AdditionalServiceRepository;
 use App\Repository\Groups\BoardServiceRepository;
@@ -15,6 +16,8 @@ use App\Service\AccommodationBookingService;
 use Doctrine\ORM\EntityManagerInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\Form\FormError;
+use Symfony\Component\Form\FormInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Attribute\Route;
@@ -121,7 +124,15 @@ class EditController extends AbstractController
                 }
             }
 
-            $this->bookingService->refreshPriceSnapshot($booking);
+            if (!$this->refreshPriceSnapshot($form, $booking)) {
+                // The submitted changes stay on the entity but are never flushed, so the form
+                // comes back filled in with the error on it. Logging is safe here: the database
+                // handler writes through DBAL, not the EntityManager.
+                return $this->render('admin/accommodation_booking/edit.html.twig', [
+                    'booking' => $booking,
+                    'form' => $form,
+                ]);
+            }
 
             // Editing never moves the booking on and never mails the customer: every status
             // change is its own named action (Angebot senden, bestätigen, absagen), so the
@@ -154,4 +165,31 @@ class EditController extends AbstractController
             'form' => $form,
         ]);
     }
+
+    /**
+     * The price is computed after validation, so an implausible total cannot be a constraint on
+     * the form — it is reported as one anyway, because the office's next move is to go and fix
+     * the house's prices, not to read an error page.
+     *
+     * @param FormInterface<AccommodationBooking> $form
+     */
+    private function refreshPriceSnapshot(FormInterface $form, AccommodationBooking $booking): bool
+    {
+        try {
+            $this->bookingService->refreshPriceSnapshot($booking);
+
+            return true;
+        } catch (ImplausibleBookingPriceException $e) {
+            $this->logger->error('Refused to store an implausible accommodation booking total', [
+                'exception' => $e,
+                'id' => $booking->getId(),
+                'accommodation' => $booking->getAccommodation()?->getCalendarCode(),
+                'paxCount' => $booking->getPaxCount(),
+                'nights' => $booking->getNights(),
+            ]);
+            $form->addError(new FormError(ImplausibleBookingPriceException::FORM_ERROR_MESSAGE));
+
+            return false;
+        }
+    }
 }
diff --git a/src/Controller/Groups/Booking/Step4Controller.php b/src/Controller/Groups/Booking/Step4Controller.php
index e6134221..f2a9d0a5 100644
--- a/src/Controller/Groups/Booking/Step4Controller.php
+++ b/src/Controller/Groups/Booking/Step4Controller.php
@@ -8,6 +8,7 @@ use App\Entity\Groups\Accommodation;
 use App\Entity\Groups\AdditionalService;
 use App\Entity\Groups\BoardService;
 use App\Exception\AccommodationSessionNotFoundException;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\AccommodationBookingConfirmationType;
 use App\Form\AccommodationInquiryConfirmationType;
 use App\Form\Model\AccommodationBookingDto;
@@ -16,6 +17,7 @@ use App\Model\AccommodationBookingContext;
 use App\Service\AccommodationBookingService;
 use App\Service\AccommodationSessionManager;
 use App\Service\AccommodationTermsUrlProvider;
+use Psr\Log\LoggerInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Attribute\Route;
@@ -28,6 +30,7 @@ class Step4Controller extends AbstractController
         private readonly AccommodationBookingService $bookingService,
         private readonly AccommodationSessionManager $sessionManager,
         private readonly AccommodationTermsUrlProvider $termsUrlProvider,
+        private readonly LoggerInterface $logger,
     ) {
     }
 
@@ -51,7 +54,9 @@ class Step4Controller extends AbstractController
             }
 
             $dto->forceInquiry = true;
-            $this->persistBooking($request, $dto, $accommodation, $services);
+            if (null !== $failure = $this->persistBooking($request, $dto, $accommodation, $services)) {
+                return $failure;
+            }
 
             return $this->redirectToRoute('app_groups_booking_success');
         }
@@ -102,7 +107,9 @@ class Step4Controller extends AbstractController
 
         if ($confirmationForm->isSubmitted() && $confirmationForm->isValid()) {
             $services = $this->bookingService->loadAvailableServices($dto, $accommodation);
-            $this->persistBooking($request, $dto, $accommodation, $services);
+            if (null !== $failure = $this->persistBooking($request, $dto, $accommodation, $services)) {
+                return $failure;
+            }
 
             return $this->htmxRedirect($request, $this->generateUrl('app_groups_booking_success'));
         }
@@ -148,12 +155,35 @@ class Step4Controller extends AbstractController
      *     groupedAdditionalServices: array<string, AdditionalService[]>,
      *     ungroupedAdditionalServices: AdditionalService[]
      * } $services
+     *
+     * @return Response|null a response to return instead of the success redirect, or null when
+     *                       the booking was stored
      */
-    private function persistBooking(Request $request, AccommodationBookingDto $dto, Accommodation $accommodation, array $services): void
+    private function persistBooking(Request $request, AccommodationBookingDto $dto, Accommodation $accommodation, array $services): ?Response
     {
         $prices = $this->bookingService->loadPrices($dto, $accommodation);
-        $booking = $this->bookingService->finalizeBooking($dto, $accommodation, $prices, $services);
+
+        try {
+            $booking = $this->bookingService->finalizeBooking($dto, $accommodation, $prices, $services);
+        } catch (ImplausibleBookingPriceException $e) {
+            // The bounded inputs are already rejected in step 2, so what is left is a mistyped
+            // catalog price for this house — nothing the customer can act on and nothing to show
+            // them an error page over. The session survives so the desk can pick the inquiry up
+            // by phone with the data still in hand.
+            $this->logger->error('Refused to store an implausible accommodation booking total', [
+                'exception' => $e,
+                'accommodation' => $accommodation->getCalendarCode(),
+                'paxCount' => $dto->paxCount,
+                'nights' => $dto->getNights(),
+            ]);
+            $this->addFlash('error', 'Die Anfrage konnte nicht abgeschlossen werden. Bitte wende dich direkt an uns — wir kümmern uns darum.');
+
+            return $this->htmxRedirect($request, $this->generateUrl('app_groups_booking_error'));
+        }
+
         $this->addFlash('groups_booking_result', $booking->getOrigin()->value);
         $this->sessionManager->clear($request);
+
+        return null;
     }
 }
diff --git a/src/Entity/Groups/AccommodationBooking.php b/src/Entity/Groups/AccommodationBooking.php
index 87bd3401..c3f98a55 100644
--- a/src/Entity/Groups/AccommodationBooking.php
+++ b/src/Entity/Groups/AccommodationBooking.php
@@ -12,11 +12,13 @@ use App\Entity\User;
 use App\Enum\Groups\AccommodationBookingOrigin;
 use App\Enum\Groups\AccommodationBookingStatus;
 use App\Enum\Groups\AdditionalServiceType;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Repository\Groups\AccommodationBookingRepository;
 use Doctrine\DBAL\Types\Types;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Uid\Uuid;
 use Symfony\Component\Validator\Constraints as Assert;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
 #[ORM\Entity(repositoryClass: AccommodationBookingRepository::class)]
 class AccommodationBooking implements BlameableEntityInterface, TimestampableEntityInterface
@@ -24,6 +26,24 @@ class AccommodationBooking implements BlameableEntityInterface, TimestampableEnt
     use BlameableEntity;
     use TimestampableEntity;
 
+    /**
+     * Plausibility ceilings for the two figures every price in the breakdown is multiplied by.
+     * Both sit above anything the group houses actually see — the largest booking on record is
+     * 150 people for 18 nights — and exist so that a mistyped year or pax count is answered with
+     * a form error rather than a price nobody meant.
+     */
+    public const int MAX_PAX = 250;
+    public const int MAX_NIGHTS = 30;
+
+    /**
+     * And the ceiling on the product of the two, in minor units: a million euros against a
+     * largest-ever booking of some 42,000. The inputs above cannot reach it, so what it catches
+     * is a mistyped catalog price, the one factor of the total that is not bounded per booking.
+     * Deliberately well inside what the INT column holds — the column's range is not a price
+     * limit, and a total that needs more room is a mistake rather than a wider column.
+     */
+    public const int MAX_TOTAL_PRICE = 100_000_000;
+
     #[ORM\Id]
     #[ORM\GeneratedValue]
     #[ORM\Column]
@@ -40,9 +60,11 @@ class AccommodationBooking implements BlameableEntityInterface, TimestampableEnt
     private ?\DateTimeImmutable $dateFrom = null;
 
     #[ORM\Column(type: Types::DATE_IMMUTABLE)]
+    #[Assert\GreaterThan(propertyPath: 'dateFrom', message: 'Das Abreisedatum muss nach dem Anreisedatum liegen.')]
     private ?\DateTimeImmutable $dateTo = null;
 
     #[ORM\Column]
+    #[Assert\Range(min: 0, max: self::MAX_PAX)]
     private int $paxCount = 0;
 
     #[ORM\Column]
@@ -68,6 +90,7 @@ class AccommodationBooking implements BlameableEntityInterface, TimestampableEnt
     #[ORM\Column(type: Types::JSON, nullable: true)]
     private ?array $priceBreakdown = null;
 
+    /** In minor units, like every other price here, and never above self::MAX_TOTAL_PRICE. */
     #[ORM\Column(nullable: true)]
     private ?int $totalPrice = null;
 
@@ -232,6 +255,25 @@ class AccommodationBooking implements BlameableEntityInterface, TimestampableEnt
         return $this->dateFrom->diff($this->dateTo)->days;
     }
 
+    /**
+     * Reported on dateTo, the field a mistyped year is corrected in — a stay of 200 years is
+     * always the departure date being wrong, never the arrival.
+     */
+    #[Assert\Callback]
+    public function validateStayLength(ExecutionContextInterface $context): void
+    {
+        if (null === $this->dateFrom || null === $this->dateTo) {
+            return;
+        }
+
+        if ($this->getNights() > self::MAX_NIGHTS) {
+            $context->buildViolation('Der Aufenthalt darf höchstens {{ max }} Nächte umfassen — bitte Anreise und Abreise prüfen.')
+                ->setParameter('{{ max }}', (string) self::MAX_NIGHTS)
+                ->atPath('dateTo')
+                ->addViolation();
+        }
+    }
+
     public function getPaxCount(): int
     {
         return $this->paxCount;
@@ -336,9 +378,17 @@ class AccommodationBooking implements BlameableEntityInterface, TimestampableEnt
         return $this->priceBreakdown;
     }
 
-    /** @param array<string, mixed> $priceBreakdown */
+    /**
+     * @param array<string, mixed> $priceBreakdown
+     *
+     * @throws ImplausibleBookingPriceException if the total is too large to be a real price
+     */
     public function setPriceSnapshot(array $priceBreakdown, int $totalPrice, string $currency, int $version): self
     {
+        if ($totalPrice > self::MAX_TOTAL_PRICE) {
+            throw new ImplausibleBookingPriceException($totalPrice, $this->paxCount, $this->getNights());
+        }
+
         $this->priceBreakdown = $priceBreakdown;
         $this->totalPrice = $totalPrice;
         $this->pricingCurrency = $currency;
diff --git a/src/Exception/ImplausibleBookingPriceException.php b/src/Exception/ImplausibleBookingPriceException.php
new file mode 100644
index 00000000..1ca45a39
--- /dev/null
+++ b/src/Exception/ImplausibleBookingPriceException.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Exception;
+
+use App\Entity\Groups\AccommodationBooking;
+
+/**
+ * Thrown when a computed accommodation booking total is too large to be a real price.
+ *
+ * The total is a product of pax count, nights and catalog prices, so a single mistyped figure
+ * anywhere in that chain can produce a number nobody could owe. Storing it is pointless — it
+ * would go out on an offer — and a signed INT column answers it with SQLSTATE 22003, which says
+ * nothing about where the mistake is. Failing here instead names the price and the inputs it
+ * came from.
+ */
+class ImplausibleBookingPriceException extends \RuntimeException
+{
+    /**
+     * What the backoffice is told. The total itself is in the log; the actionable part is the
+     * house's price rows, which is where the stray digit is.
+     */
+    public const string FORM_ERROR_MESSAGE = 'Der berechnete Gesamtpreis ist unplausibel hoch. Bitte die Preise und Leistungen des Gruppenhauses prüfen.';
+
+    public function __construct(int $totalPrice, int $paxCount, int $nights, ?\Throwable $previous = null)
+    {
+        parent::__construct(
+            sprintf(
+                'Refusing to store an implausible booking total of %d (ceiling %d, in minor units) for %d people over %d nights — check the catalog prices for this house.',
+                $totalPrice,
+                AccommodationBooking::MAX_TOTAL_PRICE,
+                $paxCount,
+                $nights,
+            ),
+            0,
+            $previous,
+        );
+    }
+}
diff --git a/src/Form/Model/AccommodationBookingDto.php b/src/Form/Model/AccommodationBookingDto.php
index 6caf404e..95fc4ae8 100644
--- a/src/Form/Model/AccommodationBookingDto.php
+++ b/src/Form/Model/AccommodationBookingDto.php
@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace App\Form\Model;
 
+use App\Entity\Groups\AccommodationBooking;
 use Symfony\Component\Validator\Constraints as Assert;
 
 class AccommodationBookingDto
@@ -16,13 +17,16 @@ class AccommodationBookingDto
 
     public ?\DateTimeImmutable $dateTo = null;
 
-    #[Assert\Positive(message: 'invalid', groups: ['step_3'])]
+    // step_2 is where the customer types these, so that is the group that has to carry the
+    // bounds: the price is computed from them on the same screen, and an implausible figure
+    // reaching step 4 only surfaces as a failure to store the booking.
+    #[Assert\Range(min: 1, max: AccommodationBooking::MAX_PAX, notInRangeMessage: 'invalid', groups: ['step_2', 'step_3'])]
     public int $paxCount = 1;
 
-    #[Assert\PositiveOrZero(message: 'invalid', groups: ['step_3'])]
+    #[Assert\Range(min: 0, max: AccommodationBooking::MAX_PAX, notInRangeMessage: 'invalid', groups: ['step_2', 'step_3'])]
     public int $minorsCount = 0;
 
-    #[Assert\PositiveOrZero(message: 'invalid', groups: ['step_3'])]
+    #[Assert\Range(min: 0, max: AccommodationBooking::MAX_PAX, notInRangeMessage: 'invalid', groups: ['step_2', 'step_3'])]
     public int $childrenCount = 0;
 
     #[Assert\NotNull(message: 'required', groups: ['step_2'])]
diff --git a/src/Service/AccommodationBookingService.php b/src/Service/AccommodationBookingService.php
index 6e10a9aa..5291980e 100644
--- a/src/Service/AccommodationBookingService.php
+++ b/src/Service/AccommodationBookingService.php
@@ -13,6 +13,7 @@ use App\Entity\Groups\AdditionalService;
 use App\Entity\Groups\BoardService;
 use App\Enum\Groups\AccommodationBookingOrigin;
 use App\Enum\Groups\AccommodationBookingStatus;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Model\AccommodationBookingDto;
 use App\Model\AccommodationBookingContext;
 use App\Model\AccommodationBookingQueryParams;
@@ -79,7 +80,8 @@ class AccommodationBookingService
     /**
      * Parses and validates raw date strings, then sets them on the DTO.
      *
-     * @throws \InvalidArgumentException if dates are invalid or dateTo ≤ dateFrom
+     * @throws \InvalidArgumentException if dates are invalid, dateTo ≤ dateFrom, or the stay
+     *                                   exceeds AccommodationBooking::MAX_NIGHTS
      */
     public function applyDates(AccommodationBookingDto $dto, string $dateFromRaw, string $dateToRaw): void
     {
@@ -94,6 +96,10 @@ class AccommodationBookingService
             throw new \InvalidArgumentException('Das Abreisedatum muss nach dem Anreisedatum liegen.');
         }
 
+        if ($dateFrom->diff($dateTo)->days > AccommodationBooking::MAX_NIGHTS) {
+            throw new \InvalidArgumentException(sprintf('Der Aufenthalt darf höchstens %d Nächte umfassen.', AccommodationBooking::MAX_NIGHTS));
+        }
+
         $dto->dateFrom = $dateFrom->setTime(0, 0, 0);
         $dto->dateTo = $dateTo->setTime(0, 0, 0);
     }
@@ -566,6 +572,9 @@ class AccommodationBookingService
      * their access link, and swapping the house underneath them would rewrite what they were
      * offered.
      * Idempotent — a no-op for a booking that is not a draft or already sits at $accommodation.
+     *
+     * @throws ImplausibleBookingPriceException if the new house prices the stay implausibly high;
+     *                                          the booking is left at its old house
      */
     public function changeAccommodation(AccommodationBooking $booking, Accommodation $accommodation): void
     {
@@ -580,8 +589,18 @@ class AccommodationBookingService
         $booking->setBoardServiceOriginalId(null);
         $booking->setAdditionalServices([]);
 
-        // Clears the snapshot by itself when the new house has no price for the booked range.
-        $this->refreshPriceSnapshot($booking);
+        try {
+            // Clears the snapshot by itself when the new house has no price for the booked range.
+            $this->refreshPriceSnapshot($booking);
+        } catch (ImplausibleBookingPriceException $e) {
+            // The swap and the dropped services are already on the managed entity, and the next
+            // flush in this request would write them without a price. Reloading the row puts the
+            // booking back at its old house so the caller can report the refusal on a record that
+            // still matches the database.
+            $this->entityManager->refresh($booking);
+
+            throw $e;
+        }
 
         $this->entityManager->flush();
     }
diff --git a/tests/Controller/Admin/AccommodationBooking/ChangeAccommodationControllerTest.php b/tests/Controller/Admin/AccommodationBooking/ChangeAccommodationControllerTest.php
index f53936d8..b2bbf132 100644
--- a/tests/Controller/Admin/AccommodationBooking/ChangeAccommodationControllerTest.php
+++ b/tests/Controller/Admin/AccommodationBooking/ChangeAccommodationControllerTest.php
@@ -8,6 +8,7 @@ use App\Controller\Admin\AccommodationBooking\ChangeAccommodationController;
 use App\Entity\Groups\Accommodation;
 use App\Entity\Groups\AccommodationBooking;
 use App\Enum\Groups\AccommodationBookingStatus;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Service\AccommodationBookingService;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
@@ -87,6 +88,36 @@ class ChangeAccommodationControllerTest extends TestCase
         self::assertSame('success', $controller->flashes[0]['type']);
     }
 
+    public function testAHouseThatPricesImplausiblyIsReportedInTheModal(): void
+    {
+        // The service leaves the booking at its old house and rethrows; the office has to see why
+        // the change did not happen, on the modal it just submitted, not as an error page.
+        $booking = $this->draft();
+
+        $bookingService = $this->createStub(AccommodationBookingService::class);
+        $bookingService->method('changeAccommodation')
+            ->willThrowException(new ImplausibleBookingPriceException(AccommodationBooking::MAX_TOTAL_PRICE + 1, 40, 2));
+
+        $field = $this->createStub(FormInterface::class);
+        $field->method('getData')->willReturn(new Accommodation());
+
+        $form = $this->createMock(FormInterface::class);
+        $form->method('handleRequest')->willReturn($form);
+        $form->method('isSubmitted')->willReturn(true);
+        $form->method('isValid')->willReturn(true);
+        $form->method('get')->with('accommodation')->willReturn($field);
+        $form->expects(self::once())->method('addError');
+
+        $controller = $this->buildController($bookingService, $form);
+
+        $response = $controller->index($booking, $this->request('POST'));
+
+        self::assertSame(Response::HTTP_OK, $response->getStatusCode());
+        self::assertFalse($response->headers->has('HX-Redirect'), 'the modal stays open on the error');
+        self::assertSame('admin/accommodation_booking/modal_change_accommodation.html.twig', $controller->renderedView);
+        self::assertSame([], $controller->flashes, 'nothing was changed, so nothing is reported as success');
+    }
+
     public function testPickingTheSameHouseIsNotReportedAsAChange(): void
     {
         $booking = $this->draft();
diff --git a/tests/Controller/Admin/AccommodationBooking/CreateControllerTest.php b/tests/Controller/Admin/AccommodationBooking/CreateControllerTest.php
index 9f71d7b2..1498aceb 100644
--- a/tests/Controller/Admin/AccommodationBooking/CreateControllerTest.php
+++ b/tests/Controller/Admin/AccommodationBooking/CreateControllerTest.php
@@ -7,6 +7,7 @@ namespace App\Tests\Controller\Admin\AccommodationBooking;
 use App\Controller\Admin\AccommodationBooking\CreateController;
 use App\Entity\Groups\AccommodationBooking;
 use App\Entity\User;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Service\AccommodationBookingService;
 use Doctrine\ORM\EntityManagerInterface;
 use PHPUnit\Framework\TestCase;
@@ -32,6 +33,37 @@ class CreateControllerTest extends TestCase
         self::assertSame($user, $controller->capturedBooking?->getManagedBy());
     }
 
+    public function testAnImplausiblePriceComesBackAsAFormErrorWithoutSaving(): void
+    {
+        // Same as on the edit form: the fix is in the house's price rows, so the office is told
+        // on the form it is standing in front of, and nothing is written.
+        $bookingService = $this->createStub(AccommodationBookingService::class);
+        $bookingService->method('refreshPriceSnapshot')
+            ->willThrowException(new ImplausibleBookingPriceException(AccommodationBooking::MAX_TOTAL_PRICE + 1, 40, 2));
+
+        $form = $this->createMock(FormInterface::class);
+        $form->method('handleRequest')->willReturn($form);
+        $form->method('isSubmitted')->willReturn(true);
+        $form->method('isValid')->willReturn(true);
+        $form->expects(self::once())->method('addError');
+
+        $entityManager = $this->createMock(EntityManagerInterface::class);
+        $entityManager->expects(self::never())->method('persist');
+        $entityManager->expects(self::never())->method('flush');
+
+        $controller = new TestableCreateController(
+            $entityManager,
+            $this->createStub(LoggerInterface::class),
+            $bookingService,
+            $form,
+            new User('manager@example.test'),
+        );
+
+        $response = $controller->index(Request::create('/admin/accommodation-booking/create', 'POST'));
+
+        self::assertSame(Response::HTTP_OK, $response->getStatusCode(), 'the modal is re-rendered, not redirected');
+    }
+
     private function buildController(?UserInterface $user): TestableCreateController
     {
         $form = $this->createStub(FormInterface::class);
diff --git a/tests/Controller/Admin/AccommodationBooking/EditControllerTest.php b/tests/Controller/Admin/AccommodationBooking/EditControllerTest.php
index 45d12bf8..e3d457a3 100644
--- a/tests/Controller/Admin/AccommodationBooking/EditControllerTest.php
+++ b/tests/Controller/Admin/AccommodationBooking/EditControllerTest.php
@@ -8,6 +8,7 @@ use App\Controller\Admin\AccommodationBooking\EditController;
 use App\Entity\Groups\AccommodationBooking;
 use App\Entity\User;
 use App\Enum\Groups\AccommodationBookingStatus;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Repository\Groups\AdditionalServiceRepository;
 use App\Repository\Groups\BoardServiceRepository;
 use App\Repository\UserRepository;
@@ -46,6 +47,39 @@ class EditControllerTest extends TestCase
         self::assertSame($status, $booking->getStatus(), 'editing leaves the status where it was');
     }
 
+    public function testAnImplausiblePriceComesBackAsAFormErrorWithoutSaving(): void
+    {
+        // The office can fix this — in the house's price rows — so it belongs on the form rather
+        // than on an error page, and nothing may be flushed in the meantime.
+        $bookingService = $this->createStub(AccommodationBookingService::class);
+        $bookingService->method('refreshPriceSnapshot')
+            ->willThrowException(new ImplausibleBookingPriceException(AccommodationBooking::MAX_TOTAL_PRICE + 1, 40, 2));
+
+        $form = $this->createMock(FormInterface::class);
+        $form->method('handleRequest')->willReturn($form);
+        $form->method('isSubmitted')->willReturn(true);
+        $form->method('isValid')->willReturn(true);
+        $form->method('has')->willReturn(false);
+        $form->expects(self::once())->method('addError');
+
+        $entityManager = $this->createMock(EntityManagerInterface::class);
+        $entityManager->expects(self::never())->method('flush');
+
+        $controller = new TestableEditController(
+            $entityManager,
+            $this->createStub(LoggerInterface::class),
+            $this->createStub(BoardServiceRepository::class),
+            $this->createStub(AdditionalServiceRepository::class),
+            $this->createStub(UserRepository::class),
+            $bookingService,
+            $form,
+        );
+
+        $response = $controller->index(new AccommodationBooking(), Request::create('/admin/accommodation-booking/1/edit', 'POST'));
+
+        self::assertSame(Response::HTTP_OK, $response->getStatusCode(), 'the form is re-rendered, not redirected');
+    }
+
     /**
      * @return iterable<string, array{AccommodationBookingStatus}>
      */
diff --git a/tests/Controller/Groups/Booking/Step4ControllerTest.php b/tests/Controller/Groups/Booking/Step4ControllerTest.php
index a89e98af..54cb22d1 100644
--- a/tests/Controller/Groups/Booking/Step4ControllerTest.php
+++ b/tests/Controller/Groups/Booking/Step4ControllerTest.php
@@ -8,11 +8,13 @@ use App\Controller\Groups\Booking\Step4Controller;
 use App\Entity\Groups\Accommodation;
 use App\Entity\Groups\AccommodationBooking;
 use App\Enum\Groups\AccommodationBookingOrigin;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Model\AccommodationBookingDto;
 use App\Service\AccommodationBookingService;
 use App\Service\AccommodationSessionManager;
 use App\Service\AccommodationTermsUrlProvider;
 use PHPUnit\Framework\TestCase;
+use Psr\Log\NullLogger;
 use Symfony\Component\Form\FormInterface;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 use Symfony\Component\HttpFoundation\Request;
@@ -302,6 +304,96 @@ class Step4ControllerTest extends TestCase
         self::assertNull($sessionManager->getDto($request));
     }
 
+    public function testConfirmPostEndsOnTheErrorPageWhenThePriceIsImplausible(): void
+    {
+        // A mistyped catalog price is the one way an implausible total still gets computed, and
+        // the customer must not meet it as a 500 — SQLSTATE 22003 on /admin is what started this.
+        $dto = new AccommodationBookingDto();
+        $dto->currentStep = 4;
+        $dto->accommodationId = 1;
+
+        $session = new Session(new MockArraySessionStorage());
+        $request = Request::create('/groups/booking/step-4/confirm', 'POST');
+        $request->setSession($session);
+        $request->headers->set('HX-Request', 'true');
+
+        $sessionManager = new AccommodationSessionManager();
+        $sessionManager->save($request, $dto);
+
+        $accommodation = (new Accommodation())
+            ->setName('Hotel')
+            ->setCalendarCode('HOTEL')
+            ->setMaxAdolescentAge(17);
+
+        $bookingService = $this->createMock(AccommodationBookingService::class);
+        $bookingService->method('loadAccommodation')->with(1)->willReturn($accommodation);
+        $bookingService->method('loadAvailableServices')->willReturn([
+            'boardServices' => [],
+            'additionalServices' => [],
+            'groupedAdditionalServices' => [],
+            'ungroupedAdditionalServices' => [],
+        ]);
+        $bookingService->method('loadPrices')->willReturn([]);
+        $bookingService->method('finalizeBooking')
+            ->willThrowException(new ImplausibleBookingPriceException(AccommodationBooking::MAX_TOTAL_PRICE + 1, 40, 2));
+
+        $confirmationForm = $this->createStub(FormInterface::class);
+        $confirmationForm->method('handleRequest')->willReturnSelf();
+        $confirmationForm->method('isSubmitted')->willReturn(true);
+        $confirmationForm->method('isValid')->willReturn(true);
+
+        $controller = new TestableStep4Controller($bookingService, $sessionManager, $confirmationForm);
+
+        $response = $controller->confirm($request);
+
+        self::assertSame('/app_groups_booking_error', $response->headers->get('HX-Redirect'));
+        // The session survives: the desk still has the inquiry to pick up by phone.
+        self::assertNotNull($sessionManager->getDto($request));
+    }
+
+    public function testIndexPostEndsOnTheErrorPageWhenThePriceIsImplausible(): void
+    {
+        $dto = new AccommodationBookingDto();
+        $dto->currentStep = 4;
+        $dto->accommodationId = 1;
+
+        $session = new Session(new MockArraySessionStorage());
+        $request = Request::create('/groups/booking/step-4', 'POST');
+        $request->setSession($session);
+
+        $sessionManager = new AccommodationSessionManager();
+        $sessionManager->save($request, $dto);
+
+        $accommodation = (new Accommodation())
+            ->setName('Hotel')
+            ->setCalendarCode('HOTEL')
+            ->setMaxAdolescentAge(17);
+
+        $bookingService = $this->createMock(AccommodationBookingService::class);
+        $bookingService->method('loadAccommodation')->with(1)->willReturn($accommodation);
+        $bookingService->method('loadAvailableServices')->willReturn([
+            'boardServices' => [],
+            'additionalServices' => [],
+            'groupedAdditionalServices' => [],
+            'ungroupedAdditionalServices' => [],
+        ]);
+        $bookingService->method('loadPrices')->willReturn([]);
+        $bookingService->method('finalizeBooking')
+            ->willThrowException(new ImplausibleBookingPriceException(AccommodationBooking::MAX_TOTAL_PRICE + 1, 40, 2));
+
+        $inquiryForm = $this->createStub(FormInterface::class);
+        $inquiryForm->method('handleRequest')->willReturnSelf();
+        $inquiryForm->method('isSubmitted')->willReturn(true);
+        $inquiryForm->method('isValid')->willReturn(true);
+
+        $controller = new TestableStep4Controller($bookingService, $sessionManager, $inquiryForm);
+
+        $response = $controller->index($request);
+
+        self::assertInstanceOf(RedirectResponse::class, $response);
+        self::assertSame('/app_groups_booking_error', $response->getTargetUrl());
+    }
+
     public function testConfirmPostInvalidReRendersModalWithoutPersisting(): void
     {
         $dto = new AccommodationBookingDto();
@@ -358,6 +450,7 @@ final class TestableStep4Controller extends Step4Controller
             $bookingService,
             $sessionManager,
             new AccommodationTermsUrlProvider(['AT' => '', 'CH' => '', 'IT' => ''], 'https://example.test/agb/'),
+            new NullLogger(),
         );
     }
 
diff --git a/tests/Entity/Groups/AccommodationBookingTest.php b/tests/Entity/Groups/AccommodationBookingTest.php
index 72b1bfe2..0b9d1139 100644
--- a/tests/Entity/Groups/AccommodationBookingTest.php
+++ b/tests/Entity/Groups/AccommodationBookingTest.php
@@ -7,6 +7,7 @@ namespace App\Tests\Entity\Groups;
 use App\Entity\Groups\AccommodationBooking;
 use App\Enum\Groups\AccommodationBookingOrigin;
 use App\Enum\Groups\AccommodationBookingStatus;
+use App\Exception\ImplausibleBookingPriceException;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 
@@ -87,6 +88,36 @@ class AccommodationBookingTest extends TestCase
         }
     }
 
+    public function testAnImplausibleTotalIsRefusedRatherThanStored(): void
+    {
+        // The pax count and the nights are capped, so what gets here is a catalog price with a
+        // digit too many. A stored total would end up on an offer; the INT column would answer
+        // it with SQLSTATE 22003 and say nothing about the cause.
+        $booking = new AccommodationBooking();
+        $booking->setDateFrom(new \DateTimeImmutable('2026-09-23'));
+        $booking->setDateTo(new \DateTimeImmutable('2026-09-25'));
+        $booking->setPaxCount(40);
+
+        $this->expectException(ImplausibleBookingPriceException::class);
+
+        $booking->setPriceSnapshot(['total' => AccommodationBooking::MAX_TOTAL_PRICE + 1], AccommodationBooking::MAX_TOTAL_PRICE + 1, 'EUR', 1);
+    }
+
+    public function testATotalAtTheCeilingIsStillStored(): void
+    {
+        $booking = new AccommodationBooking();
+        $booking->setPriceSnapshot(['total' => AccommodationBooking::MAX_TOTAL_PRICE], AccommodationBooking::MAX_TOTAL_PRICE, 'EUR', 1);
+
+        self::assertSame(AccommodationBooking::MAX_TOTAL_PRICE, $booking->getTotalPrice());
+    }
+
+    public function testTheCeilingLeavesTheIntColumnRoomToSpare(): void
+    {
+        // The ceiling exists to keep implausible prices out, not to use up the column: a total
+        // that needs more room than this is a mistake, never a wider column.
+        self::assertLessThan(2147483647, AccommodationBooking::MAX_TOTAL_PRICE);
+    }
+
     public function testTheLabelIsIndependentOfWhereTheBookingCameFrom(): void
     {
         // Origin answers "how did this come about" and is deliberately not the same
diff --git a/tests/Form/Admin/Groups/AccommodationBookingTypeTest.php b/tests/Form/Admin/Groups/AccommodationBookingTypeTest.php
index 72bf1df8..36ad8f05 100644
--- a/tests/Form/Admin/Groups/AccommodationBookingTypeTest.php
+++ b/tests/Form/Admin/Groups/AccommodationBookingTypeTest.php
@@ -109,6 +109,60 @@ class AccommodationBookingTypeTest extends TestCase
         self::assertCount(0, $this->validate($booking, ['Default']));
     }
 
+    /**
+     * The overflow this guards against reached production as an out-of-range write on
+     * total_price: every figure in the breakdown is multiplied by the pax count and the
+     * nights, so an implausible input for either produces an implausible total.
+     */
+    public function testADepartureBeforeTheArrivalIsRejected(): void
+    {
+        $booking = $this->bookingFor('2026-09-23', '2026-09-20', 30);
+
+        $violations = $this->validate($booking, ['Default']);
+
+        self::assertCount(1, $violations);
+        self::assertSame('dateTo', $violations[0]->getPropertyPath());
+    }
+
+    public function testAMistypedYearIsRejectedRatherThanPriced(): void
+    {
+        // 2226 instead of 2026 — one wrong digit, 200 years of running costs.
+        $booking = $this->bookingFor('2026-09-23', '2226-09-25', 30);
+
+        $violations = $this->validate($booking, ['Default']);
+
+        self::assertCount(1, $violations);
+        self::assertSame('dateTo', $violations[0]->getPropertyPath());
+    }
+
+    public function testAnImplausiblePaxCountIsRejected(): void
+    {
+        $booking = $this->bookingFor('2026-09-23', '2026-09-25', AccommodationBooking::MAX_PAX + 1);
+
+        $violations = $this->validate($booking, ['Default']);
+
+        self::assertCount(1, $violations);
+        self::assertSame('paxCount', $violations[0]->getPropertyPath());
+    }
+
+    public function testTheLargestBookingOnRecordStillPasses(): void
+    {
+        // 150 people for 18 nights: the ceilings must not get in the way of real business.
+        $booking = $this->bookingFor('2026-09-23', '2026-10-11', 150);
+
+        self::assertCount(0, $this->validate($booking, ['Default']));
+    }
+
+    private function bookingFor(string $dateFrom, string $dateTo, int $paxCount): AccommodationBooking
+    {
+        $booking = new AccommodationBooking();
+        $booking->setDateFrom(new \DateTimeImmutable($dateFrom));
+        $booking->setDateTo(new \DateTimeImmutable($dateTo));
+        $booking->setPaxCount($paxCount);
+
+        return $booking;
+    }
+
     /**
      * @return string[]
      */
diff --git a/tests/Form/Model/AccommodationBookingDtoTest.php b/tests/Form/Model/AccommodationBookingDtoTest.php
new file mode 100644
index 00000000..b76fd343
--- /dev/null
+++ b/tests/Form/Model/AccommodationBookingDtoTest.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Form\Model;
+
+use App\Entity\Groups\AccommodationBooking;
+use App\Form\Model\AccommodationBookingDto;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Validator\ConstraintViolationListInterface;
+use Symfony\Component\Validator\Validation;
+
+class AccommodationBookingDtoTest extends TestCase
+{
+    /**
+     * Step 2 is the screen the customer types the head count on, and the one that prices it.
+     * Bounding it only in step_3 left the figure to surface two steps later, as a booking that
+     * could not be stored.
+     */
+    #[DataProvider('implausibleHeadCounts')]
+    public function testAnImplausibleHeadCountIsRejectedWhereItIsEntered(string $property, int $value): void
+    {
+        $dto = new AccommodationBookingDto();
+        $dto->{$property} = $value;
+
+        $properties = array_map(
+            static fn ($violation) => $violation->getPropertyPath(),
+            iterator_to_array($this->validate($dto, ['step_2'])),
+        );
+
+        self::assertContains($property, $properties);
+    }
+
+    /**
+     * @return iterable<string, array{string, int}>
+     */
+    public static function implausibleHeadCounts(): iterable
+    {
+        yield 'pax above the ceiling' => ['paxCount', AccommodationBooking::MAX_PAX + 1];
+        yield 'pax below one' => ['paxCount', 0];
+        yield 'negative pax' => ['paxCount', -5];
+        yield 'minors above the ceiling' => ['minorsCount', AccommodationBooking::MAX_PAX + 1];
+        yield 'negative minors' => ['minorsCount', -1];
+        yield 'children above the ceiling' => ['childrenCount', AccommodationBooking::MAX_PAX + 1];
+    }
+
+    public function testAFullHouseStillPasses(): void
+    {
+        $dto = new AccommodationBookingDto();
+        $dto->paxCount = AccommodationBooking::MAX_PAX;
+        $dto->minorsCount = 4;
+        $dto->childrenCount = 60;
+        $dto->selectedBoardServiceId = 1;
+
+        self::assertCount(0, $this->validate($dto, ['step_2']));
+    }
+
+    /**
+     * @param string[] $groups
+     */
+    private function validate(AccommodationBookingDto $dto, array $groups): ConstraintViolationListInterface
+    {
+        return Validation::createValidatorBuilder()
+            ->enableAttributeMapping()
+            ->getValidator()
+            ->validate($dto, null, $groups);
+    }
+}
diff --git a/tests/Service/AccommodationBookingServiceTest.php b/tests/Service/AccommodationBookingServiceTest.php
index 1392f445..6f452138 100644
--- a/tests/Service/AccommodationBookingServiceTest.php
+++ b/tests/Service/AccommodationBookingServiceTest.php
@@ -12,6 +12,7 @@ use App\Entity\Groups\AccommodationPrice;
 use App\Enum\Groups\AccommodationBookingOrigin;
 use App\Enum\Groups\AccommodationBookingStatus;
 use App\Enum\Groups\AdditionalServiceType;
+use App\Exception\ImplausibleBookingPriceException;
 use App\Form\Model\AccommodationBookingDto;
 use App\Model\AccommodationBookingQueryParams;
 use App\Repository\Groups\AccommodationPriceRepository;
@@ -65,6 +66,18 @@ class AccommodationBookingServiceTest extends TestCase
         $service->initFromParams(new AccommodationBookingQueryParams('HOTEL', '2026-02-31', '2026-03-05'));
     }
 
+    public function testApplyDatesRejectsAnImplausiblyLongStay(): void
+    {
+        // The customer picks from a calendar, so this is a hand-built URL rather than a typo —
+        // the cap is the same one the backoffice form enforces on the entity.
+        $service = $this->createServiceWithAccommodation();
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage(sprintf('Der Aufenthalt darf höchstens %d Nächte umfassen.', AccommodationBooking::MAX_NIGHTS));
+
+        $service->applyDates(new AccommodationBookingDto(), '2026-02-28', '2226-03-01');
+    }
+
     public function testIssueAccessLinkForDirectBookingSetsTimestampForDirectBooking(): void
     {
         $entityManager = $this->createMock(EntityManagerInterface::class);
@@ -962,6 +975,33 @@ class AccommodationBookingServiceTest extends TestCase
         self::assertNull($booking->getTotalPrice(), 'the frozen price belonged to the old house');
     }
 
+    public function testChangeAccommodationLeavesNothingHalfAppliedWhenTheNewHousePricesImplausibly(): void
+    {
+        // The swap and the dropped services are already on the managed entity by the time the
+        // price is computed, so a refusal has to put the row back rather than leave a booking
+        // sitting at a new house with no price.
+        $breakdown = ['total' => AccommodationBooking::MAX_TOTAL_PRICE + 1, 'currency' => 'EUR'];
+        $breakdownCalculator = $this->createStub(AccommodationBookingBreakdownCalculator::class);
+        $breakdownCalculator->method('computeCurrent')->willReturn($breakdown);
+        $breakdownCalculator->method('withDiscounts')
+            ->willReturn($breakdown + ['discounts' => [], 'discountedTotal' => AccommodationBooking::MAX_TOTAL_PRICE + 1]);
+
+        $entityManager = $this->createMock(EntityManagerInterface::class);
+        $entityManager->expects(self::once())->method('refresh');
+        $entityManager->expects(self::never())->method('flush');
+
+        $service = $this->createServiceWithAccommodation(
+            entityManager: $entityManager,
+            breakdownCalculator: $breakdownCalculator,
+        );
+
+        $booking = $this->draftWithServices();
+
+        $this->expectException(ImplausibleBookingPriceException::class);
+
+        $service->changeAccommodation($booking, (new Accommodation())->setName('Berghaus')->setCalendarCode('BERG'));
+    }
+
     public function testChangeAccommodationNoOpsForANonDraft(): void
     {
         $entityManager = $this->createMock(EntityManagerInterface::class);