diff --git a/t/lib-commit-graph.sh b/t/lib-commit-graph.sh
index 5d79e1a4e9..4d3e7f0623 100755
--- a/t/lib-commit-graph.sh
+++ b/t/lib-commit-graph.sh
@@ -32,6 +32,13 @@ graph_git_behavior() {
 graph_read_expect() {
 	OPTIONAL=""
 	NUM_CHUNKS=3
+	DIR="."
+	if test "$1" = -C
+	then
+		shift
+		DIR="$1"
+		shift
+	fi
 	if test -n "$2"
 	then
 		OPTIONAL=" $2"
@@ -47,12 +54,15 @@ graph_read_expect() {
 	then
 		OPTIONS=" read_generation_data"
 	fi
-	cat >expect <<- EOF
+	cat >"$DIR/expect" <<-EOF
 	header: 43475048 1 $(test_oid oid_version) $NUM_CHUNKS 0
 	num_commits: $1
 	chunks: oid_fanout oid_lookup commit_metadata$OPTIONAL
 	options:$OPTIONS
 	EOF
-	test-tool read-graph >output &&
-	test_cmp expect output
+	(
+		cd "$DIR" &&
+		test-tool read-graph >output &&
+		test_cmp expect output
+	)
 }