diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 265a9253bf..1c04070869 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -287,10 +287,10 @@ static void credit_people(struct strbuf *out,
 	const char *me;
 
 	if (kind == 'a') {
-		label = "\n# By ";
+		label = "By";
 		me = git_author_info(IDENT_NO_DATE);
 	} else {
-		label = "\n# Via ";
+		label = "Via";
 		me = git_committer_info(IDENT_NO_DATE);
 	}
 
@@ -300,7 +300,7 @@ static void credit_people(struct strbuf *out,
 	     (me = skip_prefix(me, them->items->string)) != NULL &&
 	     skip_prefix(me, " <")))
 		return;
-	strbuf_addstr(out, label);
+	strbuf_addf(out, "\n%c %s ", comment_line_char, label);
 	add_people_count(out, them);
 }
 
@@ -503,14 +503,18 @@ static void fmt_merge_msg_sigs(struct strbuf *out)
 		} else {
 			if (tag_number == 2) {
 				struct strbuf tagline = STRBUF_INIT;
-				strbuf_addf(&tagline, "\n# %s\n",
-					    origins.items[first_tag].string);
+				strbuf_addch(&tagline, '\n');
+				strbuf_add_commented_lines(&tagline,
+						origins.items[first_tag].string,
+						strlen(origins.items[first_tag].string));
 				strbuf_insert(&tagbuf, 0, tagline.buf,
 					      tagline.len);
 				strbuf_release(&tagline);
 			}
-			strbuf_addf(&tagbuf, "\n# %s\n",
-				    origins.items[i].string);
+			strbuf_addch(&tagbuf, '\n');
+			strbuf_add_commented_lines(&tagbuf,
+					origins.items[i].string,
+					strlen(origins.items[i].string));
 			fmt_tag_signature(&tagbuf, &sig, buf, len);
 		}
 		strbuf_release(&sig);
diff --git a/t/t6200-fmt-merge-msg.sh b/t/t6200-fmt-merge-msg.sh
index f73eceabfb..e7e945db09 100755
--- a/t/t6200-fmt-merge-msg.sh
+++ b/t/t6200-fmt-merge-msg.sh
@@ -175,6 +175,24 @@ test_expect_success 'merge.log=5 shows all 5 commits' '
 	test_cmp expected actual
 '
 
+test_expect_success '--log=5 with custom comment character' '
+	cat >expected <<-EOF &&
+	Merge branch ${apos}left${apos}
+
+	/ By Another Author (3) and A U Thor (2)
+	/ Via Another Committer
+	* left:
+	  Left #5
+	  Left #4
+	  Left #3
+	  Common #2
+	  Common #1
+	EOF
+
+	git -c core.commentchar="/" fmt-merge-msg --log=5 <.git/FETCH_HEAD >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'merge.log=0 disables shortlog' '
 	echo "Merge branch ${apos}left${apos}" >expected
 	git -c merge.log=0 fmt-merge-msg <.git/FETCH_HEAD >actual &&