diff --git a/Documentation/config.txt b/Documentation/config.txt
index a33c087cb4c448..2e3c6655f0ab45 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -544,6 +544,9 @@ core.commentchar::
 	messages consider a line that begins with this character
 	commented, and removes them after the editor returns
 	(default '#').
++
+If set to "auto", `git-commit` would select a character that is not
+the beginning character of any line in existing commit messages.
 
 sequence.editor::
 	Text editor used by `git rebase -i` for editing the rebase instruction file.
diff --git a/builtin/commit.c b/builtin/commit.c
index d28505a857dad9..99c20446352edb 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -620,6 +620,36 @@ static int author_date_is_interesting(void)
 	return author_message || force_date;
 }
 
+static void adjust_comment_line_char(const struct strbuf *sb)
+{
+	char candidates[] = "#;@!$%^&|:";
+	char *candidate;
+	const char *p;
+
+	comment_line_char = candidates[0];
+	if (!memchr(sb->buf, comment_line_char, sb->len))
+		return;
+
+	p = sb->buf;
+	candidate = strchr(candidates, *p);
+	if (candidate)
+		*candidate = ' ';
+	for (p = sb->buf; *p; p++) {
+		if ((p[0] == '\n' || p[0] == '\r') && p[1]) {
+			candidate = strchr(candidates, p[1]);
+			if (candidate)
+				*candidate = ' ';
+		}
+	}
+
+	for (p = candidates; *p == ' '; p++)
+		;
+	if (!*p)
+		die(_("unable to select a comment character that is not used\n"
+		      "in the current commit message"));
+	comment_line_char = *p;
+}
+
 static int prepare_to_commit(const char *index_file, const char *prefix,
 			     struct commit *current_head,
 			     struct wt_status *s,
@@ -773,6 +803,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	if (fwrite(sb.buf, 1, sb.len, s->fp) < sb.len)
 		die_errno(_("could not write commit template"));
 
+	if (auto_comment_line_char)
+		adjust_comment_line_char(&sb);
 	strbuf_release(&sb);
 
 	/* This checks if committer ident is explicitly given */
diff --git a/cache.h b/cache.h
index 8c6cdc29deca2e..1e4b4f06e1ee01 100644
--- a/cache.h
+++ b/cache.h
@@ -618,6 +618,7 @@ extern int precomposed_unicode;
  * that is subject to stripspace.
  */
 extern char comment_line_char;
+extern int auto_comment_line_char;
 
 enum branch_track {
 	BRANCH_TRACK_UNSPECIFIED = -1,
diff --git a/config.c b/config.c
index c227aa85177724..3c3e31448e5be3 100644
--- a/config.c
+++ b/config.c
@@ -826,9 +826,16 @@ static int git_default_core_config(const char *var, const char *value)
 	if (!strcmp(var, "core.commentchar")) {
 		const char *comment;
 		int ret = git_config_string(&comment, var, value);
-		if (!ret)
+		if (ret)
+			return ret;
+		else if (!strcasecmp(comment, "auto"))
+			auto_comment_line_char = 1;
+		else if (comment[0] && !comment[1]) {
 			comment_line_char = comment[0];
-		return ret;
+			auto_comment_line_char = 0;
+		} else
+			return error("core.commentChar should only be one character");
+		return 0;
 	}
 
 	if (!strcmp(var, "core.askpass"))
diff --git a/environment.c b/environment.c
index 37354c8d056efc..c648ac3d3af1f8 100644
--- a/environment.c
+++ b/environment.c
@@ -69,6 +69,7 @@ unsigned long pack_size_limit_cfg;
  * that is subject to stripspace.
  */
 char comment_line_char = '#';
+int auto_comment_line_char;
 
 /* Parallel index stat data preload? */
 int core_preload_index = 0;
diff --git a/t/t7502-commit.sh b/t/t7502-commit.sh
index 6465cd59afb6dc..051489ea334c96 100755
--- a/t/t7502-commit.sh
+++ b/t/t7502-commit.sh
@@ -570,4 +570,30 @@ test_expect_success 'commit --status with custom comment character' '
 	test_i18ngrep "^; Changes to be committed:" .git/COMMIT_EDITMSG
 '
 
+test_expect_success 'switch core.commentchar' '
+	test_commit "#foo" foo &&
+	GIT_EDITOR=.git/FAKE_EDITOR git -c core.commentChar=auto commit --amend &&
+	test_i18ngrep "^; Changes to be committed:" .git/COMMIT_EDITMSG
+'
+
+test_expect_success 'switch core.commentchar but out of options' '
+	cat >text <<\EOF &&
+# 1
+; 2
+@ 3
+! 4
+$ 5
+% 6
+^ 7
+& 8
+| 9
+: 10
+EOF
+	git commit --amend -F text &&
+	(
+		test_set_editor .git/FAKE_EDITOR &&
+		test_must_fail git -c core.commentChar=auto commit --amend
+	)
+'
+
 test_done
diff --git a/t/t7508-status.sh b/t/t7508-status.sh
index c987b5ed652b97..148ab9ebc2fe24 100755
--- a/t/t7508-status.sh
+++ b/t/t7508-status.sh
@@ -1350,8 +1350,7 @@ test_expect_success "status (core.commentchar with submodule summary)" '
 
 test_expect_success "status (core.commentchar with two chars with submodule summary)" '
 	test_config core.commentchar ";;" &&
-	git -c status.displayCommentPrefix=true status >output &&
-	test_i18ncmp expect output
+	test_must_fail git -c status.displayCommentPrefix=true status
 '
 
 test_expect_success "--ignore-submodules=all suppresses submodule summary" '