diff --git a/git-send-email.perl b/git-send-email.perl
index cccbf4517a..5d5169707b 100755
--- a/git-send-email.perl
+++ b/git-send-email.perl
@@ -1137,7 +1137,8 @@ foreach my $t (@files) {
 	send_message();
 
 	# set up for the next message
-	if ($chain_reply_to || !defined $reply_to || length($reply_to) == 0) {
+	if ($thread &&
+		($chain_reply_to || !defined $reply_to || length($reply_to) == 0)) {
 		$reply_to = $message_id;
 		if (length $references > 0) {
 			$references .= "\n $message_id";
diff --git a/t/t9001-send-email.sh b/t/t9001-send-email.sh
index 5bfa36eccf..8518acaca6 100755
--- a/t/t9001-send-email.sh
+++ b/t/t9001-send-email.sh
@@ -621,7 +621,7 @@ 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' '
+test_expect_success 'no in-reply-to and no threading' '
 	git send-email \
 		--dry-run \
 		--from="Example <nobody@example.com>" \