diff --git a/builtin/replace.c b/builtin/replace.c
index 935647be6b..245d3f4164 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -345,7 +345,7 @@ struct check_mergetag_data {
 	const char **argv;
 };
 
-static void check_one_mergetag(struct commit *commit,
+static int check_one_mergetag(struct commit *commit,
 			       struct commit_extra_header *extra,
 			       void *data)
 {
@@ -368,20 +368,20 @@ static void check_one_mergetag(struct commit *commit,
 		if (get_oid(mergetag_data->argv[i], &oid) < 0)
 			die(_("Not a valid object name: '%s'"), mergetag_data->argv[i]);
 		if (!oidcmp(&tag->tagged->oid, &oid))
-			return; /* found */
+			return 0; /* found */
 	}
 
 	die(_("original commit '%s' contains mergetag '%s' that is discarded; "
 	      "use --edit instead of --graft"), ref, oid_to_hex(&tag_oid));
 }
 
-static void check_mergetags(struct commit *commit, int argc, const char **argv)
+static int check_mergetags(struct commit *commit, int argc, const char **argv)
 {
 	struct check_mergetag_data mergetag_data;
 
 	mergetag_data.argc = argc;
 	mergetag_data.argv = argv;
-	for_each_mergetag(check_one_mergetag, commit, &mergetag_data);
+	return for_each_mergetag(check_one_mergetag, commit, &mergetag_data);
 }
 
 static int create_graft(int argc, const char **argv, int force)
diff --git a/commit.c b/commit.c
index ca474a7c11..2952ec987c 100644
--- a/commit.c
+++ b/commit.c
@@ -1288,17 +1288,19 @@ struct commit_extra_header *read_commit_extra_headers(struct commit *commit,
 	return extra;
 }
 
-void for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data)
+int for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data)
 {
 	struct commit_extra_header *extra, *to_free;
+	int res = 0;
 
 	to_free = read_commit_extra_headers(commit, NULL);
-	for (extra = to_free; extra; extra = extra->next) {
+	for (extra = to_free; !res && extra; extra = extra->next) {
 		if (strcmp(extra->key, "mergetag"))
 			continue; /* not a merge tag */
-		fn(commit, extra, data);
+		res = fn(commit, extra, data);
 	}
 	free_commit_extra_headers(to_free);
+	return res;
 }
 
 static inline int standard_header_field(const char *field, size_t len)
diff --git a/commit.h b/commit.h
index 0fb8271665..9000895ad9 100644
--- a/commit.h
+++ b/commit.h
@@ -291,10 +291,10 @@ extern const char *find_commit_header(const char *msg, const char *key,
 /* Find the end of the log message, the right place for a new trailer. */
 extern int ignore_non_trailer(const char *buf, size_t len);
 
-typedef void (*each_mergetag_fn)(struct commit *commit, struct commit_extra_header *extra,
+typedef int (*each_mergetag_fn)(struct commit *commit, struct commit_extra_header *extra,
 				 void *cb_data);
 
-extern void for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data);
+extern int for_each_mergetag(each_mergetag_fn fn, struct commit *commit, void *data);
 
 struct merge_remote_desc {
 	struct object *obj; /* the named object, could be a tag */
diff --git a/log-tree.c b/log-tree.c
index d1c0bedf24..f3a51a6e72 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -488,9 +488,9 @@ static int is_common_merge(const struct commit *commit)
 		&& !commit->parents->next->next);
 }
 
-static void show_one_mergetag(struct commit *commit,
-			      struct commit_extra_header *extra,
-			      void *data)
+static int show_one_mergetag(struct commit *commit,
+			     struct commit_extra_header *extra,
+			     void *data)
 {
 	struct rev_info *opt = (struct rev_info *)data;
 	struct object_id oid;
@@ -502,7 +502,7 @@ static void show_one_mergetag(struct commit *commit,
 	hash_object_file(extra->value, extra->len, type_name(OBJ_TAG), &oid);
 	tag = lookup_tag(&oid);
 	if (!tag)
-		return; /* error message already given */
+		return -1; /* error message already given */
 
 	strbuf_init(&verify_message, 256);
 	if (parse_tag_buffer(tag, extra->value, extra->len))
@@ -536,11 +536,12 @@ static void show_one_mergetag(struct commit *commit,
 
 	show_sig_lines(opt, status, verify_message.buf);
 	strbuf_release(&verify_message);
+	return 0;
 }
 
-static void show_mergetag(struct rev_info *opt, struct commit *commit)
+static int show_mergetag(struct rev_info *opt, struct commit *commit)
 {
-	for_each_mergetag(show_one_mergetag, commit, opt);
+	return for_each_mergetag(show_one_mergetag, commit, opt);
 }
 
 void show_log(struct rev_info *opt)