diff --git a/t/t6006-rev-list-format.sh b/t/t6006-rev-list-format.sh
index ebdc49c496..7e82e43a63 100755
--- a/t/t6006-rev-list-format.sh
+++ b/t/t6006-rev-list-format.sh
@@ -32,6 +32,7 @@ changed_iso88591=$(echo "$changed" | iconv -f utf-8 -t $test_encoding)
 truncate_count=20
 
 test_expect_success 'setup' '
+	test_oid_init &&
 	: >foo &&
 	git add foo &&
 	git config i18n.commitEncoding $test_encoding &&
@@ -463,9 +464,10 @@ test_expect_success '--abbrev' '
 '
 
 test_expect_success '%H is not affected by --abbrev-commit' '
+	expected=$(($(test_oid hexsz) + 1)) &&
 	git log -1 --format=%H --abbrev-commit --abbrev=20 HEAD >actual &&
 	len=$(wc -c <actual) &&
-	test $len = 41
+	test $len = $expected
 '
 
 test_expect_success '%h is not affected by --abbrev-commit' '