diff --git a/src/engine/keys.h b/src/engine/keys.h
index 00e2c051f..9a138b973 100644
--- a/src/engine/keys.h
+++ b/src/engine/keys.h
@@ -248,6 +248,7 @@ enum
 	KEY_MOUSE_8 = 330,
 	KEY_MOUSE_WHEEL_UP = 331,
 	KEY_MOUSE_WHEEL_DOWN = 332,
+	KEY_MOUSE_9 = 333,
 	KEY_LAST,
 };