diff --git a/src/proto/map.pro b/src/proto/map.pro
index cf1b31a..6da455a 100644
--- a/src/proto/map.pro
+++ b/src/proto/map.pro
@@ -18,6 +18,7 @@
 void check_map_keycodes(void);
 char_u *check_map(char_u *keys, int mode, int exact, int ign_mod, int abbr, mapblock_T **mp_ptr, int *local_ptr);
 void get_maparg(typval_T *argvars, typval_T *rettv, int exact);
+void f_mapset(typval_T *argvars, typval_T *rettv);
 void init_mappings(void);
 void add_map(char_u *map, int mode);
 int langmap_adjust_mb(int c);