diff --git a/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php b/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
index 629af455f17db..5750b01af5117 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php
@@ -256,7 +256,7 @@ public function save()
                 unset($_SESSION[$key]);
             }
         }
-        if ([$key = $this->metadataBag->getStorageKey()] === array_keys($_SESSION)) {
+        if ($_SESSION && [$key = $this->metadataBag->getStorageKey()] === array_keys($_SESSION)) {
             unset($_SESSION[$key]);
         }
 
diff --git a/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php b/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
index 3ed7ce4e04653..33d3ac06366d0 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php
@@ -321,4 +321,13 @@ public function testRegenerateInvalidSessionIdForNativeFileSessionHandler()
         $this->assertTrue($started);
         $this->assertSame('&~[', session_id());
     }
+
+    public function testSaveHandlesNullSessionGracefully()
+    {
+        $storage = $this->getStorage();
+        $_SESSION = null;
+        $storage->save();
+
+        $this->addToAssertionCount(1);
+    }
 }