diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index b259d8990a..85c271acd7 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -479,6 +479,9 @@ static int cmd_parseopt(int argc, const char **argv, const char *prefix)
 		if (!s)
 			s = help;
 
+		if (s == sb.buf)
+			die(_("missing opt-spec before option flags"));
+
 		if (s - sb.buf == 1) /* short option only */
 			o->short_name = *sb.buf;
 		else if (sb.buf[1] != ',') /* long option only */
diff --git a/t/t1502-rev-parse-parseopt.sh b/t/t1502-rev-parse-parseopt.sh
index 284fe18e72..de1d48f3ba 100755
--- a/t/t1502-rev-parse-parseopt.sh
+++ b/t/t1502-rev-parse-parseopt.sh
@@ -306,6 +306,13 @@ test_expect_success 'test --parseopt help output: "wrapped" options normal "or:"
 	test_cmp expect actual
 '
 
+test_expect_success 'test --parseopt invalid opt-spec' '
+	test_write_lines x -- "=, x" >spec &&
+	echo "fatal: missing opt-spec before option flags" >expect &&
+	test_must_fail git rev-parse --parseopt -- >out <spec 2>err &&
+	test_cmp expect err
+'
+
 test_expect_success 'test --parseopt help output: multi-line blurb after empty line' '
 	sed -e "s/^|//" >spec <<-\EOF &&
 	|cmd [--some-option]