diff --git a/src/Symfony/Component/HttpFoundation/Request.php b/src/Symfony/Component/HttpFoundation/Request.php
index a950b0a159a1..4c5260520857 100644
--- a/src/Symfony/Component/HttpFoundation/Request.php
+++ b/src/Symfony/Component/HttpFoundation/Request.php
@@ -1347,6 +1347,8 @@ public function setFormat($format, $mimeTypes)
      *  * _format request attribute
      *  * $default
      *
+     * @see getPreferredFormat
+     *
      * @param string|null $default The default format
      *
      * @return string|null The request format
@@ -1563,22 +1565,27 @@ public function isNoCache()
         return $this->headers->hasCacheControlDirective('no-cache') || 'no-cache' == $this->headers->get('Pragma');
     }
 
+    /**
+     * Gets the preferred format for the response by inspecting, in the following order:
+     *   * the request format set using setRequestFormat
+     *   * the values of the Accept HTTP header
+     *   * the content type of the body of the request.
+     */
     public function getPreferredFormat(?string $default = 'html'): ?string
     {
         if (null !== $this->preferredFormat) {
             return $this->preferredFormat;
         }
 
-        $this->preferredFormat = $this->getRequestFormat($this->getContentType());
-
-        if (null === $this->preferredFormat) {
-            foreach ($this->getAcceptableContentTypes() as $contentType) {
-                if (null !== $this->preferredFormat = $this->getFormat($contentType)) {
-                    break;
-                }
+        $preferredFormat = null;
+        foreach ($this->getAcceptableContentTypes() as $contentType) {
+            if ($preferredFormat = $this->getFormat($contentType)) {
+                break;
             }
         }
 
+        $this->preferredFormat = $this->getRequestFormat($preferredFormat ?: $this->getContentType());
+
         return $this->preferredFormat ?: $default;
     }
 
diff --git a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
index 6573da078572..500d590f7857 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
@@ -407,14 +407,14 @@ public function testGetPreferredFormat()
         $this->assertSame('json', $request->getPreferredFormat('json'));
 
         $request->setRequestFormat('atom');
-        $request->headers->set('Content-Type', 'application/json');
-        $request->headers->set('Accept', 'application/xml');
+        $request->headers->set('Accept', 'application/ld+json');
+        $request->headers->set('Content-Type', 'application/merge-patch+json');
         $this->assertSame('atom', $request->getPreferredFormat());
 
         $request = new Request();
-        $request->headers->set('Content-Type', 'application/json');
         $request->headers->set('Accept', 'application/xml');
-        $this->assertSame('json', $request->getPreferredFormat());
+        $request->headers->set('Content-Type', 'application/json');
+        $this->assertSame('xml', $request->getPreferredFormat());
 
         $request = new Request();
         $request->headers->set('Accept', 'application/xml');
diff --git a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
index 7856a77c038b..550d7ce0b071 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
@@ -504,6 +504,7 @@ public function testPrepareSetContentType()
         $response = new Response('foo');
         $request = Request::create('/');
         $request->setRequestFormat('json');
+        $request->headers->remove('accept');
 
         $response->prepare($request);