diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index 7d73f6c..1e673e3 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -25,7 +25,7 @@
 void *call_func_retlist(char_u *func, int argc, typval_T *argv);
 int eval_foldexpr(char_u *arg, int *cp);
 void ex_let(exarg_T *eap);
-void list_hashtable_vars(hashtab_T *ht, char_u *prefix, int empty, int *first);
+void list_hashtable_vars(hashtab_T *ht, char *prefix, int empty, int *first);
 char_u *get_lval(char_u *name, typval_T *rettv, lval_T *lp, int unlet, int skip, int flags, int fne_flags);
 void clear_lval(lval_T *lp);
 void *eval_for_line(char_u *arg, int *errp, char_u **nextcmdp, int skip);