diff --git a/core/modules/serialization/src/Encoder/JsonEncoder.php b/core/modules/serialization/src/Encoder/JsonEncoder.php
index 91b9b4049365..a03648e20d24 100644
--- a/core/modules/serialization/src/Encoder/JsonEncoder.php
+++ b/core/modules/serialization/src/Encoder/JsonEncoder.php
@@ -2,8 +2,6 @@
 
 namespace Drupal\serialization\Encoder;
 
-use Symfony\Component\Serializer\Encoder\DecoderInterface;
-use Symfony\Component\Serializer\Encoder\EncoderInterface;
 use Symfony\Component\Serializer\Encoder\JsonDecode;
 use Symfony\Component\Serializer\Encoder\JsonEncode;
 use Symfony\Component\Serializer\Encoder\JsonEncoder as BaseJsonEncoder;
@@ -15,7 +13,7 @@ use Symfony\Component\Serializer\Encoder\JsonEncoder as BaseJsonEncoder;
  *   This encoder should not be used directly. Rather, use the `serializer`
  *   service.
  */
-class JsonEncoder extends BaseJsonEncoder implements EncoderInterface, DecoderInterface {
+class JsonEncoder extends BaseJsonEncoder {
 
   /**
    * The formats that this Encoder supports.
@@ -28,40 +26,12 @@ class JsonEncoder extends BaseJsonEncoder implements EncoderInterface, DecoderIn
    * {@inheritdoc}
    */
   public function __construct(JsonEncode $encodingImpl = NULL, JsonDecode $decodingImpl = NULL) {
-    $this->encodingImpl = $encodingImpl ?: $this->getJsonEncode();
-    $this->decodingImpl = $decodingImpl ?: $this->getJsonDecode();
-  }
-
-  /**
-   * Instantiates a JsonEncode instance.
-   *
-   * @internal this exists to bridge Symfony 3 to Symfony 4, and can be removed
-   *   once Drupal requires Symfony 4.2 or higher.
-   */
-  private function getJsonEncode() {
     // Encode <, >, ', &, and " for RFC4627-compliant JSON, which may also be
     // embedded into HTML.
     // @see \Symfony\Component\HttpFoundation\JsonResponse
     $json_encoding_options = JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_AMP | JSON_HEX_QUOT;
-    $reflection = new \ReflectionClass(JsonEncode::class);
-    if (array_key_exists('OPTIONS', $reflection->getConstants())) {
-      return new JsonEncode([JsonEncode::OPTIONS => $json_encoding_options]);
-    }
-    return new JsonEncode($json_encoding_options);
-  }
-
-  /**
-   * Instantiates a JsonDecode instance.
-   *
-   * @internal this exists to bridge Symfony 3 to Symfony 4, and can be removed
-   *   once Drupal requires Symfony 4.2 or higher.
-   */
-  private function getJsonDecode() {
-    $reflection = new \ReflectionClass(JsonDecode::class);
-    if (array_key_exists('ASSOCIATIVE', $reflection->getConstants())) {
-      return new JsonDecode([JsonDecode::ASSOCIATIVE => TRUE]);
-    }
-    return new JsonDecode(TRUE);
+    $this->encodingImpl = $encodingImpl ?: new JsonEncode([JsonEncode::OPTIONS => $json_encoding_options]);
+    $this->decodingImpl = $decodingImpl ?: new JsonDecode([JsonDecode::ASSOCIATIVE => TRUE]);
   }
 
   /**