diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index 3e87907..5d04e01 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -10,7 +10,7 @@
 int eval_expr_to_bool(typval_T *expr, int *error);
 char_u *eval_to_string_skip(char_u *arg, exarg_T *eap, int skip);
 int skip_expr(char_u **pp);
-int skip_expr_concatenate(char_u **start, char_u **end, evalarg_T *evalarg);
+int skip_expr_concatenate(char_u **arg, char_u **start, char_u **end, evalarg_T *evalarg);
 char_u *eval_to_string(char_u *arg, int convert);
 char_u *eval_to_string_safe(char_u *arg, int use_sandbox);
 varnumber_T eval_to_number(char_u *expr);