diff --git a/src/proto/evalfunc.pro b/src/proto/evalfunc.pro
index 562a7c8..ad4b98a 100644
--- a/src/proto/evalfunc.pro
+++ b/src/proto/evalfunc.pro
@@ -6,6 +6,7 @@
 char *internal_func_name(int idx);
 int internal_func_check_arg_types(type_T **types, int idx, int argcount);
 type_T *internal_func_ret_type(int idx, int argcount, type_T **argtypes);
+int internal_func_is_map(int idx);
 int check_internal_func(int idx, int argcount);
 int call_internal_func(char_u *name, int argcount, typval_T *argvars, typval_T *rettv);
 void call_internal_func_by_idx(int idx, typval_T *argvars, typval_T *rettv);