diff --git a/src/Metadata/CacheKey.php b/src/Metadata/CacheKey.php
new file mode 100644
index 00000000..95f07492
--- /dev/null
+++ b/src/Metadata/CacheKey.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\Hydrator\Metadata;
+
+use function hash;
+
+/**
+ * PSR-6 and PSR-16 reserve the characters {}()/\@: and only guarantee keys up to 64 characters,
+ * so class names are hashed instead of being used as they are.
+ *
+ * @internal
+ */
+final class CacheKey
+{
+    /** @param class-string $class */
+    public static function forClass(string $class): string
+    {
+        return 'hydrator_metadata_' . hash('xxh128', $class);
+    }
+}
diff --git a/src/Metadata/ClassMetadata.php b/src/Metadata/ClassMetadata.php
index 56927930..7d811ad9 100644
--- a/src/Metadata/ClassMetadata.php
+++ b/src/Metadata/ClassMetadata.php
@@ -110,7 +110,11 @@ public function __serialize(): array
     /** @param serialized $data */
     public function __unserialize(array $data): void
     {
-        $this->reflection = new ReflectionClass($data['className']);
+        /** @var class-string<T> $className */
+        $className = $data['className'];
+
+        $this->reflection = new ReflectionClass($className);
+        $this->className = $className;
         $this->normalizer = $data['normalizer'];
         $this->properties = $data['properties'];
         $this->lazy = $data['lazy'];
diff --git a/src/Metadata/Psr16MetadataFactory.php b/src/Metadata/Psr16MetadataFactory.php
index 603e674f..f8ec5901 100644
--- a/src/Metadata/Psr16MetadataFactory.php
+++ b/src/Metadata/Psr16MetadataFactory.php
@@ -23,16 +23,15 @@ public function __construct(
      */
     public function metadata(string $class): ClassMetadata
     {
-        /** @var ?ClassMetadata<T> $metadata */
-        $metadata = $this->cache->get($class);
+        $metadata = $this->cache->get(CacheKey::forClass($class));
 
-        if ($metadata !== null) {
+        if ($metadata instanceof ClassMetadata && $metadata->className === $class) {
             return $metadata;
         }
 
         $metadata = $this->metadataFactory->metadata($class);
 
-        $this->cache->set($class, $metadata);
+        $this->cache->set(CacheKey::forClass($class), $metadata);
 
         return $metadata;
     }
diff --git a/src/Metadata/Psr6MetadataFactory.php b/src/Metadata/Psr6MetadataFactory.php
index f2cf0b5a..907eca1e 100644
--- a/src/Metadata/Psr6MetadataFactory.php
+++ b/src/Metadata/Psr6MetadataFactory.php
@@ -23,13 +23,14 @@ public function __construct(
      */
     public function metadata(string $class): ClassMetadata
     {
-        $item = $this->cache->getItem($class);
+        $item = $this->cache->getItem(CacheKey::forClass($class));
 
         if ($item->isHit()) {
-            /** @var ClassMetadata<T> $data */
             $data = $item->get();
 
-            return $data;
+            if ($data instanceof ClassMetadata && $data->className === $class) {
+                return $data;
+            }
         }
 
         $metadata = $this->metadataFactory->metadata($class);
diff --git a/tests/Unit/Metadata/CacheKeyTest.php b/tests/Unit/Metadata/CacheKeyTest.php
new file mode 100644
index 00000000..42d6476b
--- /dev/null
+++ b/tests/Unit/Metadata/CacheKeyTest.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\Hydrator\Tests\Unit\Metadata;
+
+use Patchlevel\Hydrator\Metadata\CacheKey;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(CacheKey::class)]
+final class CacheKeyTest extends TestCase
+{
+    public function testForClass(): void
+    {
+        self::assertSame(
+            'hydrator_metadata_461ebb84f6b57aacd859c578c8ae216c',
+            CacheKey::forClass(ProfileCreated::class),
+        );
+    }
+}
diff --git a/tests/Unit/Metadata/ClassMetadataTest.php b/tests/Unit/Metadata/ClassMetadataTest.php
index 2802f298..3f47237c 100644
--- a/tests/Unit/Metadata/ClassMetadataTest.php
+++ b/tests/Unit/Metadata/ClassMetadataTest.php
@@ -4,14 +4,19 @@
 
 namespace Patchlevel\Hydrator\Tests\Unit\Metadata;
 
+use Patchlevel\Hydrator\Metadata\AttributeMetadataFactory;
 use Patchlevel\Hydrator\Metadata\ClassMetadata;
 use Patchlevel\Hydrator\Metadata\PropertyMetadata;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 use ReflectionClass;
 use ReflectionProperty;
 use Symfony\Component\TypeInfo\Type;
 
+use function serialize;
+use function unserialize;
+
 #[CoversClass(ClassMetadata::class)]
 final class ClassMetadataTest extends TestCase
 {
@@ -41,4 +46,15 @@ public function testPropertiesHashmap(): void
         self::assertSame($fooMetadata, $classMetadata->properties['foo']);
         self::assertSame($barMetadata, $classMetadata->properties['bar']);
     }
+
+    public function testSerialize(): void
+    {
+        $classMetadata = (new AttributeMetadataFactory())->metadata(ProfileCreated::class);
+
+        $unserialized = unserialize(serialize($classMetadata));
+
+        self::assertInstanceOf(ClassMetadata::class, $unserialized);
+        self::assertSame(ProfileCreated::class, $unserialized->className);
+        self::assertEquals($classMetadata, $unserialized);
+    }
 }
diff --git a/tests/Unit/Metadata/PropertyMetadataTest.php b/tests/Unit/Metadata/PropertyMetadataTest.php
new file mode 100644
index 00000000..78910607
--- /dev/null
+++ b/tests/Unit/Metadata/PropertyMetadataTest.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\Hydrator\Tests\Unit\Metadata;
+
+use Patchlevel\Hydrator\Metadata\PropertyMetadata;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\Email;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\EmailNormalizer;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use ReflectionProperty;
+use Symfony\Component\TypeInfo\Type;
+
+use function serialize;
+use function unserialize;
+
+#[CoversClass(PropertyMetadata::class)]
+final class PropertyMetadataTest extends TestCase
+{
+    public function testSerialize(): void
+    {
+        $propertyMetadata = new PropertyMetadata(
+            new ReflectionProperty(ProfileCreated::class, 'email'),
+            Type::object(Email::class),
+            'email_field',
+            new EmailNormalizer(),
+            ['foo' => 'bar'],
+        );
+
+        $unserialized = unserialize(serialize($propertyMetadata));
+
+        self::assertInstanceOf(PropertyMetadata::class, $unserialized);
+        self::assertSame('email', $unserialized->propertyName);
+        self::assertEquals($propertyMetadata, $unserialized);
+    }
+}
diff --git a/tests/Unit/Metadata/Psr16MetadataFactoryTest.php b/tests/Unit/Metadata/Psr16MetadataFactoryTest.php
index 6f356bc8..4fd5740a 100644
--- a/tests/Unit/Metadata/Psr16MetadataFactoryTest.php
+++ b/tests/Unit/Metadata/Psr16MetadataFactoryTest.php
@@ -4,14 +4,19 @@
 
 namespace Patchlevel\Hydrator\Tests\Unit\Metadata;
 
+use Patchlevel\Hydrator\Metadata\AttributeMetadataFactory;
+use Patchlevel\Hydrator\Metadata\CacheKey;
 use Patchlevel\Hydrator\Metadata\ClassMetadata;
 use Patchlevel\Hydrator\Metadata\MetadataFactory;
 use Patchlevel\Hydrator\Metadata\Psr16MetadataFactory;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 use Psr\SimpleCache\CacheInterface;
 use ReflectionClass;
 use stdClass;
+use Symfony\Component\Cache\Adapter\ArrayAdapter;
+use Symfony\Component\Cache\Psr16Cache;
 
 #[CoversClass(Psr16MetadataFactory::class)]
 final class Psr16MetadataFactoryTest extends TestCase
@@ -23,7 +28,7 @@ public function testMetadataWithHit(): void
         $cache = $this->createMock(CacheInterface::class);
         $cache->expects(self::once())
             ->method('get')
-            ->with(stdClass::class)
+            ->with(CacheKey::forClass(stdClass::class))
             ->willReturn($classMetadata);
 
         $innerFactory = $this->createMock(MetadataFactory::class);
@@ -43,11 +48,37 @@ public function testMetadataWithMiss(): void
         $cache = $this->createMock(CacheInterface::class);
         $cache->expects(self::once())
             ->method('get')
-            ->with(stdClass::class)
+            ->with(CacheKey::forClass(stdClass::class))
             ->willReturn(null);
         $cache->expects(self::once())
             ->method('set')
-            ->with(stdClass::class, $classMetadata);
+            ->with(CacheKey::forClass(stdClass::class), $classMetadata);
+
+        $innerFactory = $this->createMock(MetadataFactory::class);
+        $innerFactory->expects(self::once())
+            ->method('metadata')
+            ->with(stdClass::class)
+            ->willReturn($classMetadata);
+
+        $factory = new Psr16MetadataFactory($innerFactory, $cache);
+        $result = $factory->metadata(stdClass::class);
+
+        self::assertSame($classMetadata, $result);
+    }
+
+    public function testMetadataIgnoresEntryOfOtherClass(): void
+    {
+        $otherMetadata = new ClassMetadata(new ReflectionClass(ProfileCreated::class));
+        $classMetadata = new ClassMetadata(new ReflectionClass(stdClass::class));
+
+        $cache = $this->createMock(CacheInterface::class);
+        $cache->expects(self::once())
+            ->method('get')
+            ->with(CacheKey::forClass(stdClass::class))
+            ->willReturn($otherMetadata);
+        $cache->expects(self::once())
+            ->method('set')
+            ->with(CacheKey::forClass(stdClass::class), $classMetadata);
 
         $innerFactory = $this->createMock(MetadataFactory::class);
         $innerFactory->expects(self::once())
@@ -60,4 +91,16 @@ public function testMetadataWithMiss(): void
 
         self::assertSame($classMetadata, $result);
     }
+
+    public function testMetadataWithSymfonyCache(): void
+    {
+        $cache = new Psr16Cache(new ArrayAdapter());
+        $factory = new Psr16MetadataFactory(new AttributeMetadataFactory(), $cache);
+
+        $metadata = $factory->metadata(ProfileCreated::class);
+
+        self::assertSame(ProfileCreated::class, $metadata->className);
+        self::assertTrue($cache->has(CacheKey::forClass(ProfileCreated::class)));
+        self::assertEquals($metadata, $factory->metadata(ProfileCreated::class));
+    }
 }
diff --git a/tests/Unit/Metadata/Psr6MetadataFactoryTest.php b/tests/Unit/Metadata/Psr6MetadataFactoryTest.php
index 0d6d5f24..e72762fa 100644
--- a/tests/Unit/Metadata/Psr6MetadataFactoryTest.php
+++ b/tests/Unit/Metadata/Psr6MetadataFactoryTest.php
@@ -4,15 +4,19 @@
 
 namespace Patchlevel\Hydrator\Tests\Unit\Metadata;
 
+use Patchlevel\Hydrator\Metadata\AttributeMetadataFactory;
+use Patchlevel\Hydrator\Metadata\CacheKey;
 use Patchlevel\Hydrator\Metadata\ClassMetadata;
 use Patchlevel\Hydrator\Metadata\MetadataFactory;
 use Patchlevel\Hydrator\Metadata\Psr6MetadataFactory;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 use Psr\Cache\CacheItemInterface;
 use Psr\Cache\CacheItemPoolInterface;
 use ReflectionClass;
 use stdClass;
+use Symfony\Component\Cache\Adapter\ArrayAdapter;
 
 #[CoversClass(Psr6MetadataFactory::class)]
 final class Psr6MetadataFactoryTest extends TestCase
@@ -32,7 +36,7 @@ public function testMetadataWithHit(): void
         $cache = $this->createMock(CacheItemPoolInterface::class);
         $cache->expects(self::once())
             ->method('getItem')
-            ->with(stdClass::class)
+            ->with(CacheKey::forClass(stdClass::class))
             ->willReturn($item);
 
         $innerFactory = $this->createMock(MetadataFactory::class);
@@ -60,7 +64,44 @@ public function testMetadataWithMiss(): void
         $cache = $this->createMock(CacheItemPoolInterface::class);
         $cache->expects(self::once())
             ->method('getItem')
+            ->with(CacheKey::forClass(stdClass::class))
+            ->willReturn($item);
+        $cache->expects(self::once())
+            ->method('save')
+            ->with($item);
+
+        $innerFactory = $this->createMock(MetadataFactory::class);
+        $innerFactory->expects(self::once())
+            ->method('metadata')
             ->with(stdClass::class)
+            ->willReturn($classMetadata);
+
+        $factory = new Psr6MetadataFactory($innerFactory, $cache);
+        $result = $factory->metadata(stdClass::class);
+
+        self::assertSame($classMetadata, $result);
+    }
+
+    public function testMetadataIgnoresEntryOfOtherClass(): void
+    {
+        $otherMetadata = new ClassMetadata(new ReflectionClass(ProfileCreated::class));
+        $classMetadata = new ClassMetadata(new ReflectionClass(stdClass::class));
+
+        $item = $this->createMock(CacheItemInterface::class);
+        $item->expects(self::once())
+            ->method('isHit')
+            ->willReturn(true);
+        $item->expects(self::once())
+            ->method('get')
+            ->willReturn($otherMetadata);
+        $item->expects(self::once())
+            ->method('set')
+            ->with($classMetadata);
+
+        $cache = $this->createMock(CacheItemPoolInterface::class);
+        $cache->expects(self::once())
+            ->method('getItem')
+            ->with(CacheKey::forClass(stdClass::class))
             ->willReturn($item);
         $cache->expects(self::once())
             ->method('save')
@@ -77,4 +118,16 @@ public function testMetadataWithMiss(): void
 
         self::assertSame($classMetadata, $result);
     }
+
+    public function testMetadataWithSymfonyCache(): void
+    {
+        $cache = new ArrayAdapter();
+        $factory = new Psr6MetadataFactory(new AttributeMetadataFactory(), $cache);
+
+        $metadata = $factory->metadata(ProfileCreated::class);
+
+        self::assertSame(ProfileCreated::class, $metadata->className);
+        self::assertTrue($cache->hasItem(CacheKey::forClass(ProfileCreated::class)));
+        self::assertEquals($metadata, $factory->metadata(ProfileCreated::class));
+    }
 }