Index: /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm
===================================================================
--- /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm	(revision 50533)
+++ /trunk/src/VBox/Frontends/VirtualBox/src/platform/darwin/VBoxUtils-darwin-cocoa.mm	(revision 50534)
@@ -198,8 +198,8 @@
 void darwinToggleFullscreenMode(NativeNSWindowRef pWindow)
 {
-    /* Toggle native fullscreen mode for passed pWindow.
-     * This method is available since 10.7 only. */
+    /* Toggle native fullscreen mode for passed pWindow. This method is available since 10.7 only.
+     * To automatically sync this method subsequent calls we performing it on the main (GUI) thread. */
     if ([pWindow respondsToSelector: @selector(toggleFullScreen:)])
-        [pWindow performSelector: @selector(toggleFullScreen:) withObject: (id)nil];
+        [pWindow performSelectorOnMainThread: @selector(toggleFullScreen:) withObject: (id)nil waitUntilDone :NO];
 }