diff --git a/t/t4012-diff-binary.sh b/t/t4012-diff-binary.sh
index 60c2f6c36f..daf8234614 100755
--- a/t/t4012-diff-binary.sh
+++ b/t/t4012-diff-binary.sh
@@ -64,7 +64,8 @@ test_expect_success 'apply --numstat understands diff --binary format' '
 # apply needs to be able to skip the binary material correctly
 # in order to report the line number of a corrupt patch.
 test_expect_success 'apply detecting corrupt patch correctly' '
-	 git diff | sed -e "s/-CIT/xCIT/" >broken &&
+	 git diff >output &&
+	 sed -e "s/-CIT/xCIT/" <output >broken &&
 	 if git apply --stat --summary broken 2>detected
 	 then
 		echo unhappy - should have detected an error