diff --git a/t/t6026-merge-attr.sh b/t/t6026-merge-attr.sh
index dd8f88d18782f15e35aa3105668d9a713ba9fe3b..7a6e33e6732eaf69e298b56729ba4ead9ffaee0e 100755
--- a/t/t6026-merge-attr.sh
+++ b/t/t6026-merge-attr.sh
@@ -185,7 +185,9 @@ test_expect_success 'custom merge does not lock index' '
 	git reset --hard anchor &&
 	write_script sleep-one-second.sh <<-\EOF &&
 		sleep 1 &
+		echo $! >sleep.pid
 	EOF
+	test_when_finished "kill \$(cat sleep.pid)" &&
 
 	test_write_lines >.gitattributes \
 		"* merge=ours" "text merge=sleep-one-second" &&