diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 1c81f46cbf3b9a229c285afd13dfe627c95b7460..3d728e296d3e3b76cbde00960e12f1731cabd887 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -24,16 +24,15 @@ prompt_given ()
 }
 
 test_expect_success 'basic usage requires no repo' '
-	lines=$(git difftool -h | grep ^usage: | wc -l) &&
-	test "$lines" -eq 1 &&
+	test_expect_code 129 git difftool -h >output &&
+	grep ^usage: output &&
 	# create a ceiling directory to prevent Git from finding a repo
 	mkdir -p not/repo &&
-	ceiling="$PWD/not" &&
-	lines=$(cd not/repo &&
-		GIT_CEILING_DIRECTORIES="$ceiling" git difftool -h |
-		grep ^usage: | wc -l) &&
-	test "$lines" -eq 1 &&
-	rmdir -p not/repo
+	test_when_finished rm -r not &&
+	test_expect_code 129 \
+	env GIT_CEILING_DIRECTORIES="$(pwd)/not" \
+	git -C not/repo difftool -h >output &&
+	grep ^usage: output
 '
 
 # Create a file on master and change it on branch