diff --git a/package.json b/package.json
index 7e89650e..58ea2de1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "s3utils",
-  "version": "1.17.14",
+  "version": "1.17.15",
   "engines": {
     "node": ">= 22"
   },
diff --git a/tests/unit/utils/S3UtilsMongoClient.js b/tests/unit/utils/S3UtilsMongoClient.js
index 01b5fa77..f16485d9 100644
--- a/tests/unit/utils/S3UtilsMongoClient.js
+++ b/tests/unit/utils/S3UtilsMongoClient.js
@@ -891,6 +891,39 @@ describe('S3UtilsMongoClient::_processEntryData', () => {
                 },
             },
         ],
+        [
+            'should add content-length to cold storage location and current dataStore '
+            + 'when object is restoring with string typed timestamps',
+            testBucketName,
+            true,
+            {
+                _id: 'testkey6b',
+                value: {
+                    ...objectMdTemp,
+                    dataStoreName: 'cold-location',
+                    replicationInfo: {
+                        backends: [],
+                    },
+                    archive: {
+                        archiveInfo: {},
+                        restoreRequestedAt: new Date(Date.now() - 1000).toISOString(),
+                        restoreCompletedAt: null,
+                        restoreWillExpireAt: null,
+                    },
+                },
+            },
+            locationConfig,
+            {
+                data: {
+                    account: { [testAccountCanonicalId]: 42 },
+                    bucket: { [`${testBucketName}_${testBucketCreationDate}`]: 42 },
+                    location: {
+                        'us-east-1': 42,
+                        'cold-location': 42,
+                    },
+                },
+            },
+        ],
         [
             'should add content-length to cold storage location and current dataStore '
             + 'when object is restored',
@@ -923,6 +956,38 @@ describe('S3UtilsMongoClient::_processEntryData', () => {
                 },
             },
         ],
+        [
+            'should add content-length to cold storage location and current dataStore '
+            + 'when object is restored with string typed timestamps',
+            testBucketName,
+            true,
+            {
+                _id: 'testkey6c',
+                value: {
+                    ...objectMdTemp,
+                    'replicationInfo': {
+                        backends: [],
+                    },
+                    'archive': {
+                        archiveInfo: {},
+                        restoreCompletedAt: new Date(Date.now() - 1000).toISOString(),
+                        restoreWillExpireAt: new Date(Date.now() + 1000).toISOString(),
+                    },
+                    'x-amz-storage-class': 'cold-location',
+                },
+            },
+            locationConfig,
+            {
+                data: {
+                    account: { [testAccountCanonicalId]: 42 },
+                    bucket: { [`${testBucketName}_${testBucketCreationDate}`]: 42 },
+                    location: {
+                        'us-east-1': 42,
+                        'cold-location': 42,
+                    },
+                },
+            },
+        ],
         [
             'should return error if content-length is invalid',
             testBucketName,
@@ -3174,31 +3239,55 @@ describe('S3UtilsMongoClient, cold object helpers', () => {
         assert.strictEqual(mongoTestClient._isObjectCold(coldObject), true);
     });
 
-    it('should detect a restoring object', () => {
-        const restoringObject = {
-            value: {
-                ...coldObjectMdTemp,
-                archive: new ObjectMDArchive({}, new Date(Date.now() - 5000), 10),
-                dataStoreName: 'cold-location',
-            },
-        };
-        assert.strictEqual(mongoTestClient._isObjectRestoring(restoringObject), true);
-    });
+    // Arsenal types the archive timestamps `Date | string` and stores them as
+    // given, so both forms reach these helpers.
+    describe.each([
+        ['Date', date => date],
+        ['string', date => date.toISOString()],
+    ])('with %s timestamps', (label, stored) => {
+        it('should detect a restoring object', () => {
+            const restoringObject = {
+                value: {
+                    ...coldObjectMdTemp,
+                    archive: new ObjectMDArchive({}, stored(new Date(Date.now() - 5000)), 10),
+                    dataStoreName: 'cold-location',
+                },
+            };
+            assert.strictEqual(mongoTestClient._isObjectRestoring(restoringObject), true);
+        });
 
-    it('should detect a restored object', () => {
-        const restoredObject = {
-            value: {
-                ...coldObjectMdTemp,
-                archive: new ObjectMDArchive(
-                    {},
-                    new Date(Date.now() - 5000),
-                    10,
-                    new Date(Date.now() - 1000),
-                    new Date(Date.now() + 10000),
-                ),
-                dataStoreName: 'us-east-1',
-            },
-        };
-        assert.strictEqual(mongoTestClient._isObjectRestored(restoredObject), true);
+        it('should detect a restored object', () => {
+            const restoredObject = {
+                value: {
+                    ...coldObjectMdTemp,
+                    archive: new ObjectMDArchive(
+                        {},
+                        stored(new Date(Date.now() - 5000)),
+                        10,
+                        stored(new Date(Date.now() - 1000)),
+                        stored(new Date(Date.now() + 10000)),
+                    ),
+                    dataStoreName: 'us-east-1',
+                },
+            };
+            assert.strictEqual(mongoTestClient._isObjectRestored(restoredObject), true);
+        });
+
+        it('should detect an object with an expired restore as cold', () => {
+            const expiredObject = {
+                value: {
+                    ...coldObjectMdTemp,
+                    archive: new ObjectMDArchive(
+                        {},
+                        stored(new Date(Date.now() - 90000)),
+                        10,
+                        stored(new Date(Date.now() - 80000)),
+                        stored(new Date(Date.now() - 1000)),
+                    ),
+                    dataStoreName: 'cold-location',
+                },
+            };
+            assert.strictEqual(mongoTestClient._isObjectCold(expiredObject), true);
+        });
     });
 });
diff --git a/utils/S3UtilsMongoClient.js b/utils/S3UtilsMongoClient.js
index 3934a0b9..e2b19336 100644
--- a/utils/S3UtilsMongoClient.js
+++ b/utils/S3UtilsMongoClient.js
@@ -1094,7 +1094,8 @@ class S3UtilsMongoClient extends MongoClientInterface {
      */
     _isObjectCold(entry) {
         return entry.value.archive
-            && (!entry.value.archive.restoreRequestedAt || entry.value.archive.restoreWillExpireAt <= Date.now());
+            && (!entry.value.archive.restoreRequestedAt
+                || new Date(entry.value.archive.restoreWillExpireAt) <= Date.now());
     }
 
     /**
@@ -1104,8 +1105,9 @@ class S3UtilsMongoClient extends MongoClientInterface {
      */
     _isObjectRestoring(entry) {
         return entry.value.archive
-            && entry.value.archive.restoreRequestedAt <= Date.now()
-            && (!entry.value.archive.restoreCompletedAt || entry.value.archive.restoreCompletedAt > Date.now());
+            && new Date(entry.value.archive.restoreRequestedAt) <= Date.now()
+            && (!entry.value.archive.restoreCompletedAt
+                || new Date(entry.value.archive.restoreCompletedAt) > Date.now());
     }
 
     /**
@@ -1115,8 +1117,9 @@ class S3UtilsMongoClient extends MongoClientInterface {
      */
     _isObjectRestored(entry) {
         return entry.value.archive
-            && entry.value.archive.restoreCompletedAt && (entry.value.archive.restoreCompletedAt <= Date.now())
-            && entry.value.archive.restoreWillExpireAt > Date.now();
+            && entry.value.archive.restoreCompletedAt
+            && (new Date(entry.value.archive.restoreCompletedAt) <= Date.now())
+            && new Date(entry.value.archive.restoreWillExpireAt) > Date.now();
     }
 }