diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index ce26ea4ac5..5bfa36eccf 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -621,4 +621,14 @@ test_expect_success 'in-reply-to but no threading' '
 	grep "In-Reply-To: <in-reply-id@example.com>"
 '
 
+test_expect_failure 'no in-reply-to and no threading' '
+	git send-email \
+		--dry-run \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--nothread \
+		$patches $patches >stdout &&
+	! grep "In-Reply-To: " stdout
+'
+
 test_done