diff --git a/t/t4124-apply-ws-rule.sh b/t/t4124-apply-ws-rule.sh
index 971a5a7512..0ca29821ec 100755
--- a/t/t4124-apply-ws-rule.sh
+++ b/t/t4124-apply-ws-rule.sh
@@ -52,6 +52,13 @@ test_fix () {
 
 	# find touched lines
 	$DIFF file target | sed -n -e "s/^> //p" >fixed
+	# busybox's diff(1) doesn't output normal format
+	if ! test -s fixed
+	then
+		$DIFF -u file target |
+		grep -v '^+++ target' |
+		sed -ne "/^+/s/+//p" >fixed
+	fi
 
 	# the changed lines are all expected to change
 	fixed_cnt=$(wc -l <fixed)