diff --git a/src/Symfony/Component/HttpClient/CHANGELOG.md b/src/Symfony/Component/HttpClient/CHANGELOG.md
index 7bd03aae38..95b6b10d88 100644
--- a/src/Symfony/Component/HttpClient/CHANGELOG.md
+++ b/src/Symfony/Component/HttpClient/CHANGELOG.md
@@ -15,6 +15,7 @@ CHANGELOG
  * added `TraceableHttpClient`, `HttpClientDataCollector` and `HttpClientPass` to integrate with the web profiler
  * allow enabling buffering conditionally with a Closure
  * allow option "buffer" to be a stream resource
+ * allow arbitrary values for the "json" option
 
 4.3.0
 -----
diff --git a/src/Symfony/Component/HttpClient/HttpClientTrait.php b/src/Symfony/Component/HttpClient/HttpClientTrait.php
index d691638b9f..7cb82c73e5 100644
--- a/src/Symfony/Component/HttpClient/HttpClientTrait.php
+++ b/src/Symfony/Component/HttpClient/HttpClientTrait.php
@@ -332,7 +332,7 @@ trait HttpClientTrait
     }
 
     /**
-     * @param array|\JsonSerializable $value
+     * @param mixed $value
      *
      * @throws InvalidArgumentException When the value cannot be json-encoded
      */
@@ -340,10 +340,6 @@ trait HttpClientTrait
     {
         $flags = $flags ?? (JSON_HEX_TAG | JSON_HEX_APOS | JSON_HEX_AMP | JSON_HEX_QUOT | JSON_PRESERVE_ZERO_FRACTION);
 
-        if (!\is_array($value) && !$value instanceof \JsonSerializable) {
-            throw new InvalidArgumentException(sprintf('Option "json" must be array or JsonSerializable, %s given.', \is_object($value) ? \get_class($value) : \gettype($value)));
-        }
-
         try {
             $value = json_encode($value, $flags | (\PHP_VERSION_ID >= 70300 ? \JSON_THROW_ON_ERROR : 0), $maxDepth);
         } catch (\JsonException $e) {
diff --git a/src/Symfony/Component/HttpClient/HttpOptions.php b/src/Symfony/Component/HttpClient/HttpOptions.php
index e2510d1841..1638189f64 100644
--- a/src/Symfony/Component/HttpClient/HttpOptions.php
+++ b/src/Symfony/Component/HttpClient/HttpOptions.php
@@ -86,7 +86,7 @@ class HttpOptions
     }
 
     /**
-     * @param array|\JsonSerializable $json
+     * @param mixed $json
      *
      * @return $this
      */
diff --git a/src/Symfony/Contracts/HttpClient/HttpClientInterface.php b/src/Symfony/Contracts/HttpClient/HttpClientInterface.php
index 2a89486d1b..68afa78115 100644
--- a/src/Symfony/Contracts/HttpClient/HttpClientInterface.php
+++ b/src/Symfony/Contracts/HttpClient/HttpClientInterface.php
@@ -33,11 +33,11 @@ interface HttpClientInterface
         'query' => [],          // string[] - associative array of query string values to merge with the request's URL
         'headers' => [],        // iterable|string[]|string[][] - headers names provided as keys or as part of values
         'body' => '',           // array|string|resource|\Traversable|\Closure - the callback SHOULD yield a string
-                                //   smaller than the amount requested as argument; the empty string signals EOF; when
+                                //   smaller than the amount requested as argument; the empty string signals EOF; if
                                 //   an array is passed, it is meant as a form payload of field names and values
-        'json' => null,         // array|\JsonSerializable - when set, implementations MUST set the "body" option to
-                                //   the JSON-encoded value and set the "content-type" headers to a JSON-compatible
-                                //   value if they are not defined - typically "application/json"
+        'json' => null,         // mixed - if set, implementations MUST set the "body" option to the JSON-encoded
+                                //   value and set the "content-type" header to a JSON-compatible value if it is not
+                                //   explicitly defined in the headers option - typically "application/json"
         'user_data' => null,    // mixed - any extra data to attach to the request (scalar, callable, object...) that
                                 //   MUST be available via $response->getInfo('user_data') - not used internally
         'max_redirects' => 20,  // int - the maximum number of redirects to follow; a value lower than or equal to 0