return 0;
 }
 
-static int option_read_message(struct parse_opt_ctx_t *ctx,
-                              const struct option *opt, int unset)
+static enum parse_opt_result option_read_message(struct parse_opt_ctx_t *ctx,
+                                                const struct option *opt,
+                                                const char *arg_not_used,
+                                                int unset)
 {
        struct strbuf *buf = opt->value;
        const char *arg;
 
+       BUG_ON_OPT_ARG(arg_not_used);
        if (unset)
                BUG("-F cannot be negated");
 
                option_parse_message),
        { OPTION_LOWLEVEL_CALLBACK, 'F', "file", &merge_msg, N_("path"),
                N_("read message from file"), PARSE_OPT_NONEG,
-               (parse_opt_cb *) option_read_message },
+               NULL, 0, option_read_message },
        OPT__VERBOSITY(&verbosity),
        OPT_BOOL(0, "abort", &abort_current_merge,
                N_("abort the current in-progress merge")),