diff --git a/src/proto/gui.pro b/src/proto/gui.pro
index 2dc09a1..a49ecad 100644
--- a/src/proto/gui.pro
+++ b/src/proto/gui.pro
@@ -52,6 +52,7 @@
 void gui_new_scrollbar_colors(void);
 void gui_focus_change(int in_focus);
 void gui_mouse_moved(int x, int y);
+win_T *gui_mouse_window(mouse_find_T popup);
 void gui_mouse_correct(void);
 void ex_gui(exarg_T *eap);
 int gui_find_bitmap(char_u *name, char_u *buffer, char *ext);