diff --git a/reactos/include/win32k/ntuser.h b/reactos/include/win32k/ntuser.h
index ed98b568506..f1ba4e0545f 100644
--- a/reactos/include/win32k/ntuser.h
+++ b/reactos/include/win32k/ntuser.h
@@ -220,6 +220,7 @@ NtUserCallOneParam(
 #define TWOPARAM_ROUTINE_GETSYSCOLORPENS    0x64
 #define TWOPARAM_ROUTINE_GETSYSCOLORS       0x65
 #define TWOPARAM_ROUTINE_SETSYSCOLORS       0x66
+#define TWOPARAM_ROUTINE_ROS_SHOWWINDOW     0x1000
 DWORD
 STDCALL
 NtUserCallTwoParam(