diff --git a/reactos/subsystems/win32/win32k/ntuser/winpos.c b/reactos/subsystems/win32/win32k/ntuser/winpos.c
index cca1c449b5e..e5b278d73d1 100644
--- a/reactos/subsystems/win32/win32k/ntuser/winpos.c
+++ b/reactos/subsystems/win32/win32k/ntuser/winpos.c
@@ -733,6 +733,8 @@ WinPosInternalMoveWindow(PWINDOW_OBJECT Window, INT MoveX, INT MoveY)
 {
    PWINDOW_OBJECT Child;
 
+   ASSERT(Window != Window->FirstChild);
+
    Window->Wnd->WindowRect.left += MoveX;
    Window->Wnd->WindowRect.right += MoveX;
    Window->Wnd->WindowRect.top += MoveY;