diff --git a/src/proto/evalfunc.pro b/src/proto/evalfunc.pro
index c79b59c..0986162 100644
--- a/src/proto/evalfunc.pro
+++ b/src/proto/evalfunc.pro
@@ -9,6 +9,7 @@
 void mzscheme_call_vim(char_u *name, typval_T *args, typval_T *rettv);
 float_T vim_round(float_T f);
 long do_searchpair(char_u *spat, char_u *mpat, char_u *epat, int dir, typval_T *skip, int flags, pos_T *match_pos, linenr_T lnum_stop, long time_limit);
+void f_string(typval_T *argvars, typval_T *rettv);
 char_u *get_callback(typval_T *arg, partial_T **pp);
 void free_callback(char_u *callback, partial_T *partial);
 /* vim: set ft=c : */