diff --git a/DDrawCompat/Gdi/ScrollFunctions.cpp b/DDrawCompat/Gdi/ScrollFunctions.cpp
index 9e6b19d..1bd735f 100644
--- a/DDrawCompat/Gdi/ScrollFunctions.cpp
+++ b/DDrawCompat/Gdi/ScrollFunctions.cpp
@@ -27,7 +27,7 @@ namespace
 
 		if (flags & SW_SMOOTHSCROLL)
 		{
-			flags = LOWORD(flags ^ SW_SMOOTHSCROLL);
+			flags = (LOWORD(flags) & ~SW_SMOOTHSCROLL) | SW_INVALIDATE | SW_ERASE;
 		}
 
 		int result = CALL_ORIG_FUNC(ScrollWindowEx)(