diff --git a/src/Form/Model/BookingDto.php b/src/Form/Model/BookingDto.php
index 59c4060..536f47b 100644
--- a/src/Form/Model/BookingDto.php
+++ b/src/Form/Model/BookingDto.php
@@ -378,6 +378,13 @@ class BookingDto
             $this->$key = $value;
         }
 
+        foreach ($this->participants as $participant) {
+            if ($participant instanceof ParticipantDto) {
+                // Temporary cleanup for older serialized participants restored from session.
+                $participant->normalizeBodyDimensions();
+            }
+        }
+
         // Old sessions (before c373a989) still carry a full Travel object;
         // new sessions carry only the int ID. Handle both formats.
         // TODO: Remove Travel instance branch once all pre-deploy sessions have expired
diff --git a/src/Form/Model/ParticipantDto.php b/src/Form/Model/ParticipantDto.php
index f37d70c..e3e1b0f 100644
--- a/src/Form/Model/ParticipantDto.php
+++ b/src/Form/Model/ParticipantDto.php
@@ -360,6 +360,61 @@ class ParticipantDto
         return $ageThreshold > $age;
     }
 
+    /**
+     * Normalizes body-dimension fields to canonical string values.
+     *
+     * Keeps plain integers and digit-only strings, converting them to a
+     * normalized string representation. Anything else is treated as legacy
+     * garbage and reset to null so form hydration can continue safely.
+     */
+    public function normalizeBodyDimensions(): void
+    {
+        $this->height = $this->normalizeBodyDimensionValue($this->height);
+        $this->weight = $this->normalizeBodyDimensionValue($this->weight);
+        $this->shoeSize = $this->normalizeBodyDimensionValue($this->shoeSize);
+    }
+
+    /**
+     * Restores the DTO from session/serialization data.
+     *
+     * @param array<string, mixed> $data
+     */
+    public function __unserialize(array $data): void
+    {
+        foreach ($data as $key => $value) {
+            if (false === property_exists($this, $key)) {
+                continue;
+            }
+
+            $this->$key = $value;
+        }
+
+        if (false === isset($this->address)) {
+            $this->address = new Address();
+        }
+
+        // TODO: Remove after all legacy drafts/session snapshots with body-dimension strings have expired.
+        $this->normalizeBodyDimensions();
+    }
+
+    private function normalizeBodyDimensionValue(mixed $value): ?string
+    {
+        if (true === is_int($value)) {
+            return (string) $value;
+        }
+
+        if (false === is_string($value)) {
+            return null;
+        }
+
+        $value = trim($value);
+        if ('' === $value || false === ctype_digit($value)) {
+            return null;
+        }
+
+        return (string) (int) $value;
+    }
+
     /**
      * Validates that the applicant (index 0) has a complete address.
      *
diff --git a/src/Service/BookingEditDraftMerger.php b/src/Service/BookingEditDraftMerger.php
index f586ff9..cdc2c5f 100644
--- a/src/Service/BookingEditDraftMerger.php
+++ b/src/Service/BookingEditDraftMerger.php
@@ -46,6 +46,8 @@ class BookingEditDraftMerger
         // Body dimensions
         if (true === isset($data['bodyDimensions']) && true === is_array($data['bodyDimensions'])) {
             $this->applyBodyDimensions($participant, $data['bodyDimensions']);
+            // TODO: Drop this once all legacy drafts no longer contain non-numeric body-dimension values.
+            $participant->normalizeBodyDimensions();
         }
 
         // Room assignment
diff --git a/tests/Form/Model/BookingDtoTest.php b/tests/Form/Model/BookingDtoTest.php
index f599b4a..148ad4e 100644
--- a/tests/Form/Model/BookingDtoTest.php
+++ b/tests/Form/Model/BookingDtoTest.php
@@ -6,6 +6,7 @@ namespace App\Tests\Form\Model;
 
 use App\BusProNet\Model\Travel;
 use App\Form\Model\BookingDto;
+use App\Form\Model\ParticipantDto;
 use PHPUnit\Framework\TestCase;
 
 /**
@@ -63,4 +64,27 @@ class BookingDtoTest extends TestCase
         $this->assertSame($travel, $dto->travel);
         $this->assertSame(42, $dto->travel->id);
     }
+
+    public function testUnserializeNormalizesLegacyBodyDimensionsOnParticipants(): void
+    {
+        $travel = new Travel();
+        $travel->id = 42;
+        $travel->dateFrom = new \DateTimeImmutable('2025-06-01');
+        $travel->dateTo = new \DateTimeImmutable('2025-06-08');
+
+        $participant = new ParticipantDto();
+        $participant->height = '149-157';
+        $participant->weight = '75';
+        $participant->shoeSize = '043';
+
+        $dto = new BookingDto($travel, 1);
+        $dto->participants = [$participant];
+
+        $restored = unserialize(serialize($dto));
+
+        $this->assertInstanceOf(BookingDto::class, $restored);
+        $this->assertNull($restored->participants[0]->height);
+        $this->assertSame('75', $restored->participants[0]->weight);
+        $this->assertSame('43', $restored->participants[0]->shoeSize);
+    }
 }
diff --git a/tests/Service/BookingEditDraftManagerMutabilityTest.php b/tests/Service/BookingEditDraftManagerMutabilityTest.php
index f8635ae..e2ae26e 100644
--- a/tests/Service/BookingEditDraftManagerMutabilityTest.php
+++ b/tests/Service/BookingEditDraftManagerMutabilityTest.php
@@ -422,6 +422,66 @@ class BookingEditDraftManagerMutabilityTest extends TestCase
         $this->assertSame('Updated', $mutableParticipant->firstName);
     }
 
+    public function testDraftNormalizesLegacyBodyDimensionsToNull(): void
+    {
+        $participant = new ParticipantDto();
+        $participant->height = null;
+        $participant->weight = null;
+        $participant->shoeSize = null;
+
+        $travel = $this->createTravel();
+        $dto = $this->createBookingDto($travel, [$participant]);
+
+        $draft = $this->createDraft([
+            'participants' => [
+                0 => [
+                    'bodyDimensions' => [
+                        'height' => '149-157',
+                        'weight' => '195+',
+                        'shoeSize' => 'abc',
+                    ],
+                ],
+            ],
+        ]);
+
+        $applied = $this->service->applyDraftToDto($draft, $dto, $travel);
+
+        $this->assertTrue($applied);
+        $this->assertNull($participant->height);
+        $this->assertNull($participant->weight);
+        $this->assertNull($participant->shoeSize);
+    }
+
+    public function testDraftNormalizesNumericBodyDimensionsToCanonicalStrings(): void
+    {
+        $participant = new ParticipantDto();
+        $participant->height = null;
+        $participant->weight = null;
+        $participant->shoeSize = null;
+
+        $travel = $this->createTravel();
+        $dto = $this->createBookingDto($travel, [$participant]);
+
+        $draft = $this->createDraft([
+            'participants' => [
+                0 => [
+                    'bodyDimensions' => [
+                        'height' => '180',
+                        'weight' => '75',
+                        'shoeSize' => '043',
+                    ],
+                ],
+            ],
+        ]);
+
+        $applied = $this->service->applyDraftToDto($draft, $dto, $travel);
+
+        $this->assertTrue($applied);
+        $this->assertSame('180', $participant->height);
+        $this->assertSame('75', $participant->weight);
+        $this->assertSame('43', $participant->shoeSize);
+    }
+
     // --- Helpers ---
 
     private function createService(int $id, string $label = 'Test', bool $isTransportation = false): Service