diff --git a/src/proto/strings.pro b/src/proto/strings.pro
index a72e1ff..8924a25 100644
--- a/src/proto/strings.pro
+++ b/src/proto/strings.pro
@@ -23,6 +23,7 @@
 char_u *concat_str(char_u *str1, char_u *str2);
 char_u *string_quote(char_u *str, int function);
 long string_count(char_u *haystack, char_u *needle, int ic);
+void string_reverse(char_u *str, typval_T *rettv);
 void string_filter_map(char_u *str, filtermap_T filtermap, typval_T *expr, typval_T *rettv);
 void string_reduce(typval_T *argvars, typval_T *expr, typval_T *rettv);
 void f_byteidx(typval_T *argvars, typval_T *rettv);