diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index c2df7a2..551dacb 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -60,6 +60,7 @@
 int eval_isnamec1(int c);
 int eval_isdictc(int c);
 char_u *char_from_string(char_u *str, varnumber_T index);
+char_u *string_slice(char_u *str, varnumber_T first, varnumber_T last);
 int handle_subscript(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int verbose);
 int item_copy(typval_T *from, typval_T *to, int deep, int copyID);
 void echo_one(typval_T *rettv, int with_space, int *atstart, int *needclr);