diff --git a/win32ss/include/ntuser.h b/win32ss/include/ntuser.h
index 38076513db2..339076b4984 100644
--- a/win32ss/include/ntuser.h
+++ b/win32ss/include/ntuser.h
@@ -2129,7 +2129,7 @@ BOOL
 NTAPI
 NtUserEndDeferWindowPosEx(
     HDWP WinPosInfo,
-    DWORD Unknown1);
+    BOOL bAsync);
 
 BOOL
 NTAPI
diff --git a/win32ss/user/ntuser/winpos.c b/win32ss/user/ntuser/winpos.c
index da70805ed9c..4586d2357dc 100644
--- a/win32ss/user/ntuser/winpos.c
+++ b/win32ss/user/ntuser/winpos.c
@@ -3164,12 +3164,12 @@ NtUserChildWindowFromPointEx(HWND hwndParent,
  */
 BOOL APIENTRY
 NtUserEndDeferWindowPosEx(HDWP WinPosInfo,
-                          DWORD Unknown1)
+                          BOOL bAsync)
 {
    BOOL Ret;
    TRACE("Enter NtUserEndDeferWindowPosEx\n");
    UserEnterExclusive();
-   Ret = IntEndDeferWindowPosEx(WinPosInfo, (BOOL)Unknown1);
+   Ret = IntEndDeferWindowPosEx(WinPosInfo, bAsync);
    TRACE("Leave NtUserEndDeferWindowPosEx, ret=%i\n", Ret);
    UserLeave();
    return Ret;
diff --git a/win32ss/user/user32/windows/mdi.c b/win32ss/user/user32/windows/mdi.c
index c93e541b463..2849c0d6612 100644
--- a/win32ss/user/user32/windows/mdi.c
+++ b/win32ss/user/user32/windows/mdi.c
@@ -2190,7 +2190,7 @@ CascadeWindows(HWND hwndParent, UINT wFlags, LPCRECT lpRect,
         ++ret;
     }
 
-    EndDeferWindowPos(hDWP);
+    NtUserEndDeferWindowPosEx(hDWP, TRUE);
 
     if (hwndPrev)
         SetForegroundWindow(hwndPrev);
@@ -2384,7 +2384,7 @@ TileWindows(HWND hwndParent, UINT wFlags, LPCRECT lpRect,
         ++ret;
     }
 
-    EndDeferWindowPos(hDWP);
+    NtUserEndDeferWindowPosEx(hDWP, TRUE);
 
     if (hwndPrev)
         SetForegroundWindow(hwndPrev);
diff --git a/win32ss/user/user32/windows/window.c b/win32ss/user/user32/windows/window.c
index 8aa237ba397..cf7f5c9ccc0 100644
--- a/win32ss/user/user32/windows/window.c
+++ b/win32ss/user/user32/windows/window.c
@@ -645,7 +645,7 @@ DeferWindowPos(HDWP hWinPosInfo,
 BOOL WINAPI
 EndDeferWindowPos(HDWP hWinPosInfo)
 {
-    return NtUserEndDeferWindowPosEx(hWinPosInfo, 0);
+    return NtUserEndDeferWindowPosEx(hWinPosInfo, FALSE);
 }