diff --git a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
index 00d2e3b00ef83..d3036da0c6c0d 100644
--- a/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/AbstractObjectNormalizer.php
@@ -1159,6 +1159,10 @@ private function getMappedClass(array $data, string $class, array $context): str
             throw NotNormalizableValueException::createForUnexpectedDataType(\sprintf('Type property "%s" not found for the abstract object "%s".', $mapping->getTypeProperty(), $class), null, ['string'], isset($context['deserialization_path']) ? $context['deserialization_path'].'.'.$mapping->getTypeProperty() : $mapping->getTypeProperty(), false);
         }
 
+        if (!is_string($type) && (!is_object($type) || !method_exists($type, '__toString'))) {
+            throw NotNormalizableValueException::createForUnexpectedDataType(\sprintf('The type property "%s" for the abstract object "%s" must be a string.', $mapping->getTypeProperty(), $class), $type, ['string'], isset($context['deserialization_path']) ? $context['deserialization_path'].'.'.$mapping->getTypeProperty() : $mapping->getTypeProperty(), false);
+        }
+
         if (null === $mappedClass = $mapping->getClassForType($type)) {
             throw NotNormalizableValueException::createForUnexpectedDataType(\sprintf('The type "%s" is not a valid value.', $type), $type, ['string'], isset($context['deserialization_path']) ? $context['deserialization_path'].'.'.$mapping->getTypeProperty() : $mapping->getTypeProperty(), true);
         }
diff --git a/src/Symfony/Component/Serializer/Tests/Fixtures/Attributes/AbstractDummyFirstChild.php b/src/Symfony/Component/Serializer/Tests/Fixtures/Attributes/AbstractDummyFirstChild.php
index b5cd2faba24ee..cb9cb0abbe347 100644
--- a/src/Symfony/Component/Serializer/Tests/Fixtures/Attributes/AbstractDummyFirstChild.php
+++ b/src/Symfony/Component/Serializer/Tests/Fixtures/Attributes/AbstractDummyFirstChild.php
@@ -16,6 +16,7 @@
 class AbstractDummyFirstChild extends AbstractDummy
 {
     public $bar;
+    public $baz;
 
     /** @var DummyFirstChildQuux|null */
     public $quux;
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
index 270b65f33ef66..bc9a956e4781d 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php
@@ -12,6 +12,7 @@
 namespace Symfony\Component\Serializer\Tests\Normalizer;
 
 use PHPUnit\Framework\TestCase;
+use stdClass;
 use Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor;
 use Symfony\Component\PropertyInfo\Extractor\PhpStanExtractor;
 use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
@@ -525,6 +526,74 @@ private function getDenormalizerForStringCollection()
         return $denormalizer;
     }
 
+    /**
+     * @dataProvider provideInvalidDiscriminatorTypes
+     */
+    public function testDenormalizeWithDiscriminatorMapHandlesInvalidTypeValue(mixed $typeValue, bool $shouldFail)
+    {
+        if ($shouldFail) {
+            $this->expectException(NotNormalizableValueException::class);
+            $this->expectExceptionMessage(
+                'The type property "type" for the abstract object "Symfony\Component\Serializer\Tests\Fixtures\Attributes\AbstractDummy" must be a string.'
+            );
+        }
+
+        $factory = new ClassMetadataFactory(new AttributeLoader());
+
+        $loaderMock = new class implements ClassMetadataFactoryInterface {
+            public function getMetadataFor($value): ClassMetadataInterface
+            {
+                if (AbstractDummy::class === $value) {
+                    return new ClassMetadata(
+                        AbstractDummy::class,
+                        new ClassDiscriminatorMapping('type', [
+                            'first' => AbstractDummyFirstChild::class,
+                            'second' => AbstractDummySecondChild::class,
+                        ])
+                    );
+                }
+
+                throw new InvalidArgumentException();
+            }
+
+            public function hasMetadataFor($value): bool
+            {
+                return AbstractDummy::class === $value;
+            }
+        };
+
+        $discriminatorResolver = new ClassDiscriminatorFromClassMetadata($loaderMock);
+        $normalizer = new AbstractObjectNormalizerDummy($factory, null, new PhpDocExtractor(), $discriminatorResolver);
+        $serializer = new Serializer([$normalizer]);
+        $normalizer->setSerializer($serializer);
+        $normalizedData = $normalizer->denormalize(['foo' => 'foo', 'baz' => 'baz', 'quux' => ['value' => 'quux'], 'type' => $typeValue], AbstractDummy::class);
+
+        if ($shouldFail) {
+            $this->fail('Expected exception not thrown.');
+        }
+
+        $this->assertInstanceOf(DummyFirstChildQuux::class, $normalizedData->quux);
+    }
+
+    public function provideInvalidDiscriminatorTypes()
+    {
+        $toStringObject = new class() {
+            public function __toString()
+            {
+                return 'first';
+            }
+        };
+
+        return [
+            [[], true],
+            [new StdClass(), true],
+            [123, true],
+            [false, true],
+            ['first', false],
+            [$toStringObject, false],
+        ];
+    }
+
     public function testDenormalizeWithDiscriminatorMapUsesCorrectClassname()
     {
         $factory = new ClassMetadataFactory(new AttributeLoader());