N_("Please enter a commit message to explain why this merge is necessary,\n"
    "especially if it merges an updated upstream into a topic branch.\n"
    "\n"
-   "Lines starting with '#' will be ignored, and an empty message aborts\n"
+   "Lines starting with '%c' will be ignored, and an empty message aborts\n"
    "the commit.\n");
 
 static void prepare_to_commit(struct commit_list *remoteheads)
 {
        struct strbuf msg = STRBUF_INIT;
-       const char *comment = _(merge_editor_comment);
        strbuf_addbuf(&msg, &merge_msg);
        strbuf_addch(&msg, '\n');
        if (0 < option_edit)
-               strbuf_add_lines(&msg, "# ", comment, strlen(comment));
+               strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
        write_merge_msg(&msg);
-       run_hook(get_index_file(), "prepare-commit-msg",
-                git_path("MERGE_MSG"), "merge", NULL, NULL);
+       if (run_hook(get_index_file(), "prepare-commit-msg",
+                    git_path("MERGE_MSG"), "merge", NULL, NULL))
+               abort_commit(remoteheads, NULL);
        if (0 < option_edit) {
                if (launch_editor(git_path("MERGE_MSG"), NULL, NULL))
                        abort_commit(remoteheads, NULL);
                        memset(&opts, 0, sizeof(opts));
                        opts.add_title = !have_message;
                        opts.shortlog_len = shortlog_len;
+                       opts.credit_people = (0 < option_edit);
 
                        fmt_merge_msg(&merge_names, &merge_msg, &opts);
                        if (merge_msg.len)