diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 81cf118cb6..bc95db9e08 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -629,7 +629,7 @@ test_expect_success 'corrupt commit-graph write (broken parent)' '
 		empty="$(git mktree </dev/null)" &&
 		cat >broken <<-EOF &&
 		tree $empty
-		parent 0000000000000000000000000000000000000000
+		parent $ZERO_OID
 		author whatever <whatever@example.com> 1234 -0000
 		committer whatever <whatever@example.com> 1234 -0000
 
@@ -650,7 +650,7 @@ test_expect_success 'corrupt commit-graph write (missing tree)' '
 		cd repo &&
 		tree="$(git mktree </dev/null)" &&
 		cat >broken <<-EOF &&
-		parent 0000000000000000000000000000000000000000
+		parent $ZERO_OID
 		author whatever <whatever@example.com> 1234 -0000
 		committer whatever <whatever@example.com> 1234 -0000