diff --git a/git-send-email.perl b/git-send-email.perl
index adf7ecb5c3..09fe3d95c4 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -821,7 +821,7 @@ Date: $date
 Message-Id: $message_id
 X-Mailer: git-send-email $gitversion
 ";
-	if ($thread && $reply_to) {
+	if ($reply_to) {
 
 		$header .= "In-Reply-To: $reply_to\n";
 		$header .= "References: $references\n";
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 4df4f965cb..d7634187aa 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -455,4 +455,15 @@ test_expect_success 'feed two files' '
 	test "z$(sed -n -e 2p subjects)" = "zSubject: [PATCH 2/2] add master"
 '
 
+test_expect_success 'in-reply-to but no threading' '
+	git send-email \
+		--dry-run \
+		--from="Example <nobody@example.com>" \
+		--to=nobody@example.com \
+		--in-reply-to="<in-reply-id@example.com>" \
+		--no-thread \
+		$patches |
+	grep "In-Reply-To: <in-reply-id@example.com>"
+'
+
 test_done