diff --git a/src/proto/window.pro b/src/proto/window.pro
index 8fa8661..70d6b06 100644
--- a/src/proto/window.pro
+++ b/src/proto/window.pro
@@ -1,4 +1,5 @@
 /* window.c */
+int window_layout_locked(void);
 win_T *prevwin_curwin(void);
 void do_window(int nchar, long Prenum, int xchar);
 void get_wincmd_addr_type(char_u *arg, exarg_T *eap);