diff --git a/reactos/subsystems/win32/win32k/ntuser/vis.c b/reactos/subsystems/win32/win32k/ntuser/vis.c
index 05c3583b7c0..0f30e35fbdb 100644
--- a/reactos/subsystems/win32/win32k/ntuser/vis.c
+++ b/reactos/subsystems/win32/win32k/ntuser/vis.c
@@ -43,7 +43,7 @@ VIS_ComputeVisibleRegion(
 
    Wnd = Window->Wnd;
 
-   if (!(Wnd->Style & WS_VISIBLE))
+   if (!Wnd || !(Wnd->Style & WS_VISIBLE))
    {
       return NULL;
    }
diff --git a/reactos/subsystems/win32/win32k/ntuser/winpos.c b/reactos/subsystems/win32/win32k/ntuser/winpos.c
index a94fe20e744..ba19166ed19 100644
--- a/reactos/subsystems/win32/win32k/ntuser/winpos.c
+++ b/reactos/subsystems/win32/win32k/ntuser/winpos.c
@@ -759,6 +759,9 @@ BOOL FASTCALL
 WinPosFixupFlags(WINDOWPOS *WinPos, PWINDOW_OBJECT Window)
 {
    PWINDOW Wnd = Window->Wnd;
+
+   if (!Wnd) return FALSE;
+
    if (Wnd->Style & WS_VISIBLE)
    {
       WinPos->flags &= ~SWP_SHOWWINDOW;