diff --git a/widget/windows/nsWindow.cpp b/widget/windows/nsWindow.cpp
index 672dbc8bf0d4b8..41d8da885fa6a5 100644
--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -4686,7 +4686,9 @@ nsWindow::ProcessMessage(UINT msg, WPARAM& wParam, LPARAM& lParam,
         break;
 
       // let the dwm handle nc painting on glass
-      if(nsUXThemeData::CheckForCompositor())
+      // Never allow native painting if we are on fullscreen
+      if(mSizeMode != nsSizeMode_Fullscreen &&
+         nsUXThemeData::CheckForCompositor())
         break;
 
       if (wParam == TRUE) {