diff --git a/src/proto/ex_docmd.pro b/src/proto/ex_docmd.pro
index 1955ccf..3ed1523 100644
--- a/src/proto/ex_docmd.pro
+++ b/src/proto/ex_docmd.pro
@@ -10,6 +10,7 @@
 void undo_cmdmod(exarg_T *eap, int save_msg_scroll);
 int parse_cmd_address(exarg_T *eap, char **errormsg, int silent);
 int checkforcmd(char_u **pp, char *cmd, int len);
+char_u *skip_option_env_lead(char_u *start);
 char_u *find_ex_command(exarg_T *eap, int *full, void *(*lookup)(char_u *, size_t, cctx_T *), cctx_T *cctx);
 int modifier_len(char_u *cmd);
 int cmd_exists(char_u *name);