struct option options[] = {
                OPT_BOOLEAN(0, "log",     &merge_summary, "populate log with the shortlog"),
                OPT_BOOLEAN(0, "summary", &merge_summary, "alias for --log"),
-               OPT_STRING('F', "file",   &inpath, "file", "file to read from"),
+               OPT_FILENAME('F', "file", &inpath, "file to read from"),
                OPT_END()
        };
 
        int ret;
 
        git_config(fmt_merge_msg_config, NULL);
-       argc = parse_options(argc, argv, options, fmt_merge_msg_usage, 0);
+       argc = parse_options(argc, argv, prefix, options, fmt_merge_msg_usage,
+                            0);
        if (argc > 0)
                usage_with_options(fmt_merge_msg_usage, options);