diff --git a/core/modules/serialization/src/Normalizer/NormalizerBase.php b/core/modules/serialization/src/Normalizer/NormalizerBase.php
index 8779b1a1b6..3c61c0db6a 100644
--- a/core/modules/serialization/src/Normalizer/NormalizerBase.php
+++ b/core/modules/serialization/src/Normalizer/NormalizerBase.php
@@ -13,7 +13,7 @@
   /**
    * The interface or class that this Normalizer supports.
    *
-   * @var string|array
+   * @var string|string[]
    */
   protected $supportedInterfaceOrClass;
 
@@ -42,11 +42,23 @@ public function supportsNormalization($data, $format = NULL) {
   }
 
   /**
-   * Implements \Symfony\Component\Serializer\Normalizer\DenormalizerInterface::supportsDenormalization()
+   * Checks whether the given data type can be denormalized.
    *
    * This class doesn't implement DenormalizerInterface, but most of its child
    * classes do, so this method is implemented at this level to reduce code
    * duplication.
+   *
+   * @param mixed $data
+   *   Data to denormalize from.
+   * @param string|object $type
+   *   The type to which the data should be denormalized.
+   * @param string $format
+   *   The format(s) being deserialized from.
+   *
+   * @return bool
+   *   A state of check.
+   *
+   * @see \Symfony\Component\Serializer\Normalizer\DenormalizerInterface::supportsDenormalization()
    */
   public function supportsDenormalization($data, $type, $format = NULL) {
     // If the format is not supported return now.
@@ -56,11 +68,21 @@ public function supportsDenormalization($data, $type, $format = NULL) {
 
     $supported = (array) $this->supportedInterfaceOrClass;
 
-    $subclass_check = function ($name) use ($type) {
-      return (class_exists($name) || interface_exists($name)) && is_subclass_of($type, $name, TRUE);
-    };
+    if (
+      // Object types should be checked.
+      is_object($type) ||
+      // There's also possible to pass a fully qualified class name (FQCN)
+      // as an argument. We'll perceive a string as an object type if it
+      // contains backslashes, which are indicators of the PHP namespace,
+      // or if the "class_exists()" explicitly returns "TRUE".
+      (is_string($type) && (strpos($type, '\\') !== FALSE || class_exists($type)))
+    ) {
+      return (bool) array_filter($supported, function ($name) use ($type) {
+        return (class_exists($name) || interface_exists($name)) && is_a($type, $name, TRUE);
+      });
+    }
 
-    return in_array($type, $supported) || array_filter($supported, $subclass_check);
+    return in_array($type, $supported, TRUE);
   }
 
   /**
diff --git a/core/modules/serialization/tests/src/Unit/Normalizer/NormalizerBaseTest.php b/core/modules/serialization/tests/src/Unit/Normalizer/NormalizerBaseTest.php
index 63b9bf714d..e0a68b9373 100644
--- a/core/modules/serialization/tests/src/Unit/Normalizer/NormalizerBaseTest.php
+++ b/core/modules/serialization/tests/src/Unit/Normalizer/NormalizerBaseTest.php
@@ -61,6 +61,64 @@ public function providerTestSupportsNormalization() {
     ];
   }
 
+  /**
+   * Tests the supportsDenormalization method.
+   *
+   * @param bool $expected_return
+   *   The expected boolean return value from supportDenormalization.
+   * @param string|int|float $type
+   *   An interface, class or value to check for denormalization support.
+   * @param string|string[] $format
+   *   (optional) An interface, class or value the denormalization is supported
+   *   for.
+   *
+   * @dataProvider providerTestSupportsDenormalization
+   */
+  public function testSupportsDenormalization($expected_return, $type, $format = NULL) {
+    /** @var \Drupal\Tests\serialization\Unit\Normalizer\TestNormalizerBase $normalizer_base */
+    $normalizer_base = $this->getMockForAbstractClass(TestNormalizerBase::class);
+
+    if (isset($format)) {
+      $normalizer_base->setSupportedInterfaceOrClass($format);
+    }
+
+    $this->assertSame($expected_return, $normalizer_base->supportsDenormalization(NULL, $type));
+  }
+
+  /**
+   * Data provider for testSupportsDenormalization.
+   *
+   * @return array[]
+   *   An array of provider data for testSupportsDenormalization.
+   */
+  public function providerTestSupportsDenormalization() {
+    $formats = [
+      1.10,
+      '123',
+      '1.13',
+      'Ns\Of\MissingClass',
+      'stdClass',
+      NormalizerBase::class,
+    ];
+
+    return [
+      [FALSE, '1.10', $formats],
+      [TRUE, 1.10, $formats],
+      [FALSE, 123, $formats],
+      [TRUE, '123', $formats],
+      [FALSE, 1.13, $formats],
+      [TRUE, '1.13', $formats],
+      // A non-existent class must fail.
+      [FALSE, 'Ns\Of\MissingClass', $formats],
+      // Check the same class.
+      [TRUE, \stdClass::class, $formats],
+      // Check the instance.
+      [TRUE, new \stdClass(), $formats],
+      // Check the subclass.
+      [TRUE, TestNormalizerBase::class, $formats],
+    ];
+  }
+
 }
 
 /**