diff --git a/src/proto/gui_x11.pro b/src/proto/gui_x11.pro
index 66f192a..f8abb07 100644
--- a/src/proto/gui_x11.pro
+++ b/src/proto/gui_x11.pro
@@ -11,7 +11,7 @@
 extern void gui_mch_exit __ARGS((int rc));
 extern int gui_mch_get_winpos __ARGS((int *x, int *y));
 extern void gui_mch_set_winpos __ARGS((int x, int y));
-extern void gui_mch_set_shellsize __ARGS((int width, int height, int min_width, int min_height, int base_width, int base_height));
+extern void gui_mch_set_shellsize __ARGS((int width, int height, int min_width, int min_height, int base_width, int base_height, int direction));
 extern void gui_mch_get_screen_dimensions __ARGS((int *screen_w, int *screen_h));
 extern int gui_mch_init_font __ARGS((char_u *font_name, int do_fontset));
 extern GuiFont gui_mch_get_font __ARGS((char_u *name, int giveErrorIfMissing));