diff --git a/reactos/include/psdk/htmlhelp.h b/reactos/include/psdk/htmlhelp.h
index edfae94b787..dc2181da08d 100644
--- a/reactos/include/psdk/htmlhelp.h
+++ b/reactos/include/psdk/htmlhelp.h
@@ -48,6 +48,7 @@
 #define HH_SET_EXCLUSIVE_FILTER 0x19
 #define HH_INITIALIZE           0x1C
 #define HH_UNINITIALIZE         0x1D
+#define HH_SAFE_DISPLAY_TOPIC   0x20
 #define HH_PRETRANSLATEMESSAGE  0xFD
 #define HH_SET_GLOBAL_PROPERTY  0xFC