diff --git a/src/msgraph_core/tasks/large_file_upload.py b/src/msgraph_core/tasks/large_file_upload.py
index 882b2ad6..048ba5f6 100644
--- a/src/msgraph_core/tasks/large_file_upload.py
+++ b/src/msgraph_core/tasks/large_file_upload.py
@@ -73,11 +73,18 @@ def upload_session_expired(self, upload_session: Optional[Parsable] = None) -> b
         if expiry is None:
             raise ValueError("Expiry is None")
         if isinstance(expiry, str):
-            then = datetime.strptime(expiry, "%Y-%m-%dT%H:%M:%S")
+            normalized_expiry = expiry[:-1] + '+00:00' if expiry.endswith('Z') else expiry
+            then = datetime.fromisoformat(normalized_expiry)
         elif isinstance(expiry, datetime):
             then = expiry
         else:
             raise ValueError("Expiry is not a string or datetime")
+
+        if then.tzinfo is not None and then.tzinfo.utcoffset(then) is not None:
+            then = then.astimezone(timezone.utc)
+        else:
+            then = then.replace(tzinfo=timezone.utc)
+
         interval = now - then
         if not isinstance(interval, timedelta):
             raise ValueError("Interval is not a timedelta")
diff --git a/tests/tasks/test_large_file_upload.py b/tests/tasks/test_large_file_upload.py
new file mode 100644
index 00000000..c2b187e6
--- /dev/null
+++ b/tests/tasks/test_large_file_upload.py
@@ -0,0 +1,64 @@
+from datetime import datetime, timedelta, timezone
+from io import BytesIO
+from unittest.mock import Mock
+
+import pytest
+
+from msgraph_core.models import LargeFileUploadSession
+from msgraph_core.tasks.large_file_upload import LargeFileUploadTask
+
+
+def create_upload_task(expiration_date_time):
+    upload_session = LargeFileUploadSession(
+        expiration_date_time=expiration_date_time,
+        next_expected_ranges=['0-'],
+        upload_url='https://example.org/upload',
+    )
+    return LargeFileUploadTask(upload_session, Mock(), BytesIO(b'test payload'))
+
+
+def test_upload_session_expired_with_naive_datetime():
+    expiration_date_time = (datetime.now(timezone.utc) - timedelta(minutes=5)).replace(tzinfo=None)
+    task = create_upload_task(expiration_date_time)
+
+    assert task.upload_session_expired() is True
+
+
+def test_upload_session_not_expired_with_naive_datetime():
+    expiration_date_time = (datetime.now(timezone.utc) + timedelta(minutes=5)).replace(tzinfo=None)
+    task = create_upload_task(expiration_date_time)
+
+    assert task.upload_session_expired() is False
+
+
+def test_upload_session_expired_with_offset_aware_datetime():
+    expiration_date_time = datetime.now(
+        timezone(timedelta(hours=-5))
+    ) - timedelta(minutes=5)
+    task = create_upload_task(expiration_date_time)
+
+    assert task.upload_session_expired() is True
+
+
+def test_upload_session_not_expired_with_offset_aware_datetime():
+    expiration_date_time = datetime.now(
+        timezone(timedelta(hours=-5))
+    ) + timedelta(minutes=5)
+    task = create_upload_task(expiration_date_time)
+
+    assert task.upload_session_expired() is False
+
+
+@pytest.mark.parametrize(
+    ('expiration_date_time', 'expected'),
+    [
+        ((datetime.now(timezone.utc) - timedelta(minutes=5)).isoformat().replace('+00:00', 'Z'), True),
+        ((datetime.now(timezone.utc) + timedelta(minutes=5)).astimezone(
+            timezone(timedelta(hours=2))
+        ).isoformat(), False),
+    ],
+)
+def test_upload_session_expired_with_iso8601_string(expiration_date_time, expected):
+    task = create_upload_task(expiration_date_time)
+
+    assert task.upload_session_expired() is expected