diff --git a/src/Symfony/Component/HttpFoundation/Response.php b/src/Symfony/Component/HttpFoundation/Response.php
index 95e432bc2a610..f658e97f3ab5e 100644
--- a/src/Symfony/Component/HttpFoundation/Response.php
+++ b/src/Symfony/Component/HttpFoundation/Response.php
@@ -1075,12 +1075,16 @@ public function isNotModified(Request $request)
             return false;
         }
 
-        $lastModified = $request->headers->get('If-Modified-Since');
-        $notModified = false;
+        $notModified   = false;
+        $lastModified  = $this->headers->get('Last-Modified');
+        $modifiedSince = $request->headers->get('If-Modified-Since');
+
         if ($etags = $request->getEtags()) {
-            $notModified = (in_array($this->getEtag(), $etags) || in_array('*', $etags)) && (!$lastModified || $this->headers->get('Last-Modified') == $lastModified);
-        } elseif ($lastModified) {
-            $notModified = $lastModified == $this->headers->get('Last-Modified');
+            $notModified = in_array($this->getEtag(), $etags) || in_array('*', $etags);
+        }
+
+        if ($modifiedSince && $lastModified) {
+            $notModified = strtotime($modifiedSince) >= strtotime($lastModified) && (!$etags || $notModified);
         }
 
         if ($notModified) {
diff --git a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
index a84809ad7ad54..010cfece8d805 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/ResponseTest.php
@@ -141,16 +141,24 @@ public function testIsNotModifiedNotSafe()
 
     public function testIsNotModifiedLastModified()
     {
+        $before   = 'Sun, 25 Aug 2013 18:32:31 GMT';
         $modified = 'Sun, 25 Aug 2013 18:33:31 GMT';
+        $after    = 'Sun, 25 Aug 2013 19:33:31 GMT';
 
         $request = new Request();
         $request->headers->set('If-Modified-Since', $modified);
 
         $response = new Response();
+
         $response->headers->set('Last-Modified', $modified);
+        $this->assertTrue($response->isNotModified($request));
 
+        $response->headers->set('Last-Modified', $before);
         $this->assertTrue($response->isNotModified($request));
 
+        $response->headers->set('Last-Modified', $after);
+        $this->assertFalse($response->isNotModified($request));
+
         $response->headers->set('Last-Modified', '');
         $this->assertFalse($response->isNotModified($request));
     }
@@ -175,6 +183,50 @@ public function testIsNotModifiedEtag()
         $this->assertFalse($response->isNotModified($request));
     }
 
+    public function testIsNotModifiedLastModifiedAndEtag()
+    {
+        $before   = 'Sun, 25 Aug 2013 18:32:31 GMT';
+        $modified = 'Sun, 25 Aug 2013 18:33:31 GMT';
+        $after    = 'Sun, 25 Aug 2013 19:33:31 GMT';
+        $etag     = 'randomly_generated_etag';
+
+        $request = new Request();
+        $request->headers->set('if_none_match', sprintf('%s, %s', $etag, 'etagThree'));
+        $request->headers->set('If-Modified-Since', $modified);
+
+        $response = new Response();
+
+        $response->headers->set('ETag', $etag);
+        $response->headers->set('Last-Modified', $after);
+        $this->assertFalse($response->isNotModified($request));
+
+        $response->headers->set('ETag', 'non-existent-etag');
+        $response->headers->set('Last-Modified', $before);
+        $this->assertFalse($response->isNotModified($request));
+
+        $response->headers->set('ETag', $etag);
+        $response->headers->set('Last-Modified', $modified);
+        $this->assertTrue($response->isNotModified($request));
+    }
+
+    public function testIsNotModifiedIfModifiedSinceAndEtagWithoutLastModified()
+    {
+        $modified = 'Sun, 25 Aug 2013 18:33:31 GMT';
+        $etag     = 'randomly_generated_etag';
+
+        $request = new Request();
+        $request->headers->set('if_none_match', sprintf('%s, %s', $etag, 'etagThree'));
+        $request->headers->set('If-Modified-Since', $modified);
+
+        $response = new Response();
+
+        $response->headers->set('ETag', $etag);
+        $this->assertTrue($response->isNotModified($request));
+
+        $response->headers->set('ETag', 'non-existent-etag');
+        $this->assertFalse($response->isNotModified($request));
+    }
+
     public function testIsValidateable()
     {
         $response = new Response('', 200, array('Last-Modified' => $this->createDateTimeOneHourAgo()->format(DATE_RFC2822)));