diff --git a/t/helper/test-oid-array.c b/t/helper/test-oid-array.c
index aafe398ef0..076b849cbf 100644
--- a/t/helper/test-oid-array.c
+++ b/t/helper/test-oid-array.c
@@ -1,3 +1,5 @@
+#define USE_THE_REPOSITORY_VARIABLE
+
 #include "test-tool.h"
 #include "hex.h"
 #include "oid-array.h"
@@ -17,6 +19,8 @@ int cmd__oid_array(int argc UNUSED, const char **argv UNUSED)
 	int nongit_ok;
 
 	setup_git_directory_gently(&nongit_ok);
+	if (nongit_ok)
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
 
 	while (strbuf_getline(&line, stdin) != EOF) {
 		const char *arg;
diff --git a/t/t0064-oid-array.sh b/t/t0064-oid-array.sh
index 88c89e8f48..de74b692d0 100755
--- a/t/t0064-oid-array.sh
+++ b/t/t0064-oid-array.sh
@@ -15,6 +15,24 @@ echoid () {
 	done
 }
 
+test_expect_success 'without repository' '
+	cat >expect <<-EOF &&
+	4444444444444444444444444444444444444444
+	5555555555555555555555555555555555555555
+	8888888888888888888888888888888888888888
+	aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+	EOF
+	cat >input <<-EOF &&
+	append 4444444444444444444444444444444444444444
+	append 5555555555555555555555555555555555555555
+	append 8888888888888888888888888888888888888888
+	append aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+	for_each_unique
+	EOF
+	nongit test-tool oid-array <input >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'ordered enumeration' '
 	echoid "" 44 55 88 aa >expect &&
 	{