diff --git a/lcl/include/customcontrol.inc b/lcl/include/customcontrol.inc
index 94cbd22ffa..601fc2bd7a 100644
--- a/lcl/include/customcontrol.inc
+++ b/lcl/include/customcontrol.inc
@@ -79,9 +79,14 @@ begin
 end;
 
 class procedure TCustomControl.WSRegisterClass;
+const
+  Registered : boolean = False;
 begin
+  if Registered then
+    Exit;
   inherited WSRegisterClass;
   RegisterCustomControl;
+  Registered := True;
 end;
 
 {------------------------------------------------------------------------------
diff --git a/lcl/include/scrollingwincontrol.inc b/lcl/include/scrollingwincontrol.inc
index 5a4f66a8c6..34c80cd275 100644
--- a/lcl/include/scrollingwincontrol.inc
+++ b/lcl/include/scrollingwincontrol.inc
@@ -231,9 +231,14 @@ begin
 end;
 
 class procedure TScrollingWinControl.WSRegisterClass;
+const
+  Registered : boolean = False;
 begin
+  if Registered then
+    Exit;
   inherited WSRegisterClass;
   RegisterScrollingWinControl;
+  Registered := True;
 end;
 
 procedure TScrollingWinControl.ScrollBy(DeltaX, DeltaY: Integer);