diff --git a/src/Symfony/Component/HttpFoundation/BinaryFileResponse.php b/src/Symfony/Component/HttpFoundation/BinaryFileResponse.php
index 0314621907356..177b708e8f054 100644
--- a/src/Symfony/Component/HttpFoundation/BinaryFileResponse.php
+++ b/src/Symfony/Component/HttpFoundation/BinaryFileResponse.php
@@ -150,7 +150,7 @@ public function setAutoEtag()
      * Sets the Content-Disposition header with the given filename.
      *
      * @param string $disposition      ResponseHeaderBag::DISPOSITION_INLINE or ResponseHeaderBag::DISPOSITION_ATTACHMENT
-     * @param string $filename         Optionally use this filename instead of the real name of the file
+     * @param string $filename         Optionally use this UTF-8 encoded filename instead of the real name of the file
      * @param string $filenameFallback A fallback filename, containing only ASCII characters. Defaults to an automatically encoded filename
      *
      * @return $this
@@ -162,7 +162,7 @@ public function setContentDisposition($disposition, $filename = '', $filenameFal
         }
 
         if ('' === $filenameFallback && (!preg_match('/^[\x20-\x7e]*$/', $filename) || false !== strpos($filename, '%'))) {
-            $encoding = mb_detect_encoding($filename, null, true);
+            $encoding = mb_detect_encoding($filename, null, true) ?: '8bit';
 
             for ($i = 0, $filenameLength = mb_strlen($filename, $encoding); $i < $filenameLength; ++$i) {
                 $char = mb_substr($filename, $i, 1, $encoding);
diff --git a/src/Symfony/Component/HttpFoundation/Tests/BinaryFileResponseTest.php b/src/Symfony/Component/HttpFoundation/Tests/BinaryFileResponseTest.php
index e4607201a2151..e41a2372b9df8 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/BinaryFileResponseTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/BinaryFileResponseTest.php
@@ -68,6 +68,17 @@ public function testSetContentDispositionGeneratesSafeFallbackFilename()
         $this->assertSame('attachment; filename="f__.html"; filename*=utf-8\'\'f%C3%B6%C3%B6.html', $response->headers->get('Content-Disposition'));
     }
 
+    public function testSetContentDispositionGeneratesSafeFallbackFilenameForWronglyEncodedFilename()
+    {
+        $response = new BinaryFileResponse(__FILE__);
+
+        $iso88591EncodedFilename = utf8_decode('föö.html');
+        $response->setContentDisposition(ResponseHeaderBag::DISPOSITION_ATTACHMENT, $iso88591EncodedFilename);
+
+        // the parameter filename* is invalid in this case (rawurldecode('f%F6%F6') does not provide a UTF-8 string but an ISO-8859-1 encoded one)
+        $this->assertSame('attachment; filename="f__.html"; filename*=utf-8\'\'f%F6%F6.html', $response->headers->get('Content-Disposition'));
+    }
+
     /**
      * @dataProvider provideRanges
      */