diff --git a/lcl/interfaces/qt/qtwsforms.pp b/lcl/interfaces/qt/qtwsforms.pp
index 8906ce6e71..eb9d14473a 100644
--- a/lcl/interfaces/qt/qtwsforms.pp
+++ b/lcl/interfaces/qt/qtwsforms.pp
@@ -420,7 +420,8 @@ begin
       {$endif}
 
       {$ifdef HASX11}
-      if (GetWindowManager = 'kwin') and IsOldKDEInstallation then
+      if ((QtWidgetSet.WindowManagerName = 'kwin') and IsOldKDEInstallation) or
+        (QtWidgetSet.WindowManagerName = 'xfwm4') then
       begin
         W := nil;
         ActiveWin := GetActiveWindow;