diff --git a/src/Form/Service/Abstract/AbstractParticipantFieldHandler.php b/src/Form/Service/Abstract/AbstractParticipantFieldHandler.php
index 14f8cdc..d296ea3 100644
--- a/src/Form/Service/Abstract/AbstractParticipantFieldHandler.php
+++ b/src/Form/Service/Abstract/AbstractParticipantFieldHandler.php
@@ -153,6 +153,21 @@ abstract class AbstractParticipantFieldHandler implements ParticipantFieldHandle
         return is_numeric($value) ? (int) $value : null;
     }
 
+    /**
+     * Normalizes a checkbox/form toggle value to a boolean.
+     *
+     * Form checkboxes may submit true, false, 1, 0, '1', '0', or be absent.
+     * This method treats only true, 1, and '1' as checked; everything else as unchecked.
+     *
+     * @param mixed $value The raw value from form submission
+     *
+     * @return bool True if the checkbox is considered checked, false otherwise
+     */
+    protected function normalizeCheckboxValue(mixed $value): bool
+    {
+        return true === $value || 1 === $value || '1' === $value;
+    }
+
     /**
      * Returns field state modifications that should be applied after processing.
      *
diff --git a/src/Form/Service/ParticipantBulkInsuranceFieldHandler.php b/src/Form/Service/ParticipantBulkInsuranceFieldHandler.php
index c241fcc..fcdd652 100644
--- a/src/Form/Service/ParticipantBulkInsuranceFieldHandler.php
+++ b/src/Form/Service/ParticipantBulkInsuranceFieldHandler.php
@@ -68,6 +68,6 @@ class ParticipantBulkInsuranceFieldHandler extends AbstractParticipantFieldHandl
 
         // Get checkbox value from submitted data and store it
         $bulkInsuranceBooking = $this->getFieldValue($submittedData, $this->getFieldName());
-        $participant->bulkInsuranceBooking = (bool) $bulkInsuranceBooking;
+        $participant->bulkInsuranceBooking = $this->normalizeCheckboxValue($bulkInsuranceBooking);
     }
 }
diff --git a/src/Form/Service/ParticipantInsuranceFieldHandler.php b/src/Form/Service/ParticipantInsuranceFieldHandler.php
index f6ed3c8..58f1a0a 100644
--- a/src/Form/Service/ParticipantInsuranceFieldHandler.php
+++ b/src/Form/Service/ParticipantInsuranceFieldHandler.php
@@ -334,7 +334,7 @@ class ParticipantInsuranceFieldHandler extends AbstractParticipantFieldHandler
 
         // Check if bulk insurance booking is enabled
         $bulkInsuranceBooking = $applicantData['bulkInsuranceBooking'] ?? false;
-        if (false === (bool) $bulkInsuranceBooking) {
+        if (false === $this->normalizeCheckboxValue($bulkInsuranceBooking)) {
             return false;
         }
 
diff --git a/src/Form/Service/ParticipantParkingFieldHandler.php b/src/Form/Service/ParticipantParkingFieldHandler.php
index 8a46876..11f05f3 100644
--- a/src/Form/Service/ParticipantParkingFieldHandler.php
+++ b/src/Form/Service/ParticipantParkingFieldHandler.php
@@ -66,7 +66,7 @@ class ParticipantParkingFieldHandler extends AbstractParticipantFieldHandler
         }
 
         $parkingSelected = $this->getFieldValue($submittedData, $this->getFieldName());
-        $isParkingSelected = (bool) $parkingSelected;
+        $isParkingSelected = $this->normalizeCheckboxValue($parkingSelected);
 
         // Store boolean value for backward compatibility
         $participant->parking = $isParkingSelected;
diff --git a/src/Form/Service/ParticipantRentalInsuranceFieldHandler.php b/src/Form/Service/ParticipantRentalInsuranceFieldHandler.php
index 79848a7..090bbcd 100644
--- a/src/Form/Service/ParticipantRentalInsuranceFieldHandler.php
+++ b/src/Form/Service/ParticipantRentalInsuranceFieldHandler.php
@@ -100,7 +100,7 @@ class ParticipantRentalInsuranceFieldHandler extends AbstractParticipantFieldHan
 
         // Extract checkbox value from submitted data (this comes from the rentalInsuranceSelected property)
         $rentalInsuranceSelected = $this->getFieldValue($submittedData, $this->getFieldName());
-        $isRentalInsuranceSelected = (bool) $rentalInsuranceSelected;
+        $isRentalInsuranceSelected = $this->normalizeCheckboxValue($rentalInsuranceSelected);
 
         // Store boolean value
         $participant->rentalInsuranceSelected = $isRentalInsuranceSelected;
diff --git a/tests/Form/Service/ParticipantParkingFieldHandlerTest.php b/tests/Form/Service/ParticipantParkingFieldHandlerTest.php
index ae26588..7568e65 100644
--- a/tests/Form/Service/ParticipantParkingFieldHandlerTest.php
+++ b/tests/Form/Service/ParticipantParkingFieldHandlerTest.php
@@ -37,6 +37,22 @@ class ParticipantParkingFieldHandlerTest extends TestCase
         $this->assertTrue($this->handler->shouldProcess(['some' => 'data'], BookingDto::MODE_EDIT, 5));
     }
 
+    /**
+     * @dataProvider normalizeCheckboxValueCheckedProvider
+     */
+    public function testNormalizeCheckboxValueReturnsTrueWhenChecked(mixed $value): void
+    {
+        $this->assertTrue($this->invokeNormalizeCheckboxValue($value));
+    }
+
+    /**
+     * @dataProvider normalizeCheckboxValueUncheckedProvider
+     */
+    public function testNormalizeCheckboxValueReturnsFalseWhenUnchecked(mixed $value): void
+    {
+        $this->assertFalse($this->invokeNormalizeCheckboxValue($value));
+    }
+
     public function testProcessFieldWithoutParticipant(): void
     {
         $travel = new Travel();
@@ -241,6 +257,40 @@ class ParticipantParkingFieldHandlerTest extends TestCase
         $this->assertNull($participant->parkingService);
     }
 
+    /**
+     * @return array<string, array{mixed}>
+     */
+    public static function normalizeCheckboxValueCheckedProvider(): array
+    {
+        return [
+            'true' => [true],
+            'int 1' => [1],
+            'string 1' => ['1'],
+        ];
+    }
+
+    /**
+     * @return array<string, array{mixed}>
+     */
+    public static function normalizeCheckboxValueUncheckedProvider(): array
+    {
+        return [
+            'false' => [false],
+            'int 0' => [0],
+            'string 0' => ['0'],
+            'empty string' => [''],
+            'null' => [null],
+            'non-numeric string' => ['off'],
+        ];
+    }
+
+    private function invokeNormalizeCheckboxValue(mixed $value): bool
+    {
+        $reflection = new \ReflectionMethod($this->handler, 'normalizeCheckboxValue');
+
+        return $reflection->invoke($this->handler, $value);
+    }
+
     private function createTransportationService(string $subType): Service
     {
         $service = new Service();