diff --git a/vncviewer/DesktopWindow.cxx b/vncviewer/DesktopWindow.cxx
index a4485cd..f63b16e 100644
--- a/vncviewer/DesktopWindow.cxx
+++ b/vncviewer/DesktopWindow.cxx
@@ -179,7 +179,8 @@
     // FIXME: We reassert the keyboard grabbing on focus/unfocus as FLTK
     //        releases the grab when someone calls Fl::grab(0)
   case FL_FULLSCREEN:
-    fullScreen.setParam(fullscreen_active());
+    if (event == FL_FULLSCREEN)
+      fullScreen.setParam(fullscreen_active());
 
     if (!fullscreenSystemKeys)
       break;