diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index d3d381ae285..44fd97e1aa3 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1548,7 +1548,7 @@ static const QScreen *effectiveScreen(const QWindow *w)
 
 bool QWindowsWindow::isFullScreen_sys() const
 {
-    return geometry_sys() == effectiveScreen(window())->geometry();
+    return window()->isTopLevel() && geometry_sys() == effectiveScreen(window())->geometry();
 }
 
 /*!