diff --git a/aiogoogle/auth/utils.py b/aiogoogle/auth/utils.py
index 3f15c92..be0f2cd 100644
--- a/aiogoogle/auth/utils.py
+++ b/aiogoogle/auth/utils.py
@@ -31,8 +31,9 @@ def _is_expired(expires_at):
             expires_at = _parse_isoformat(expires_at)
         else:
             expires_at = datetime.datetime.fromisoformat(expires_at)
-    utc_now = datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None)
-    if utc_now >= expires_at:
+    if expires_at.tzinfo is None:
+        expires_at = expires_at.replace(tzinfo=datetime.timezone.utc)
+    if datetime.datetime.now(datetime.timezone.utc) >= expires_at:
         return True
     else:
         return False
diff --git a/tests/test_units/test_auth/test_utils.py b/tests/test_units/test_auth/test_utils.py
index a7c910c..cd250c3 100644
--- a/tests/test_units/test_auth/test_utils.py
+++ b/tests/test_units/test_auth/test_utils.py
@@ -1,6 +1,6 @@
 import datetime
 
-from aiogoogle.auth.utils import _get_expires_at
+from aiogoogle.auth.utils import _get_expires_at, _is_expired
 
 
 def test_get_expires_at():
@@ -9,3 +9,11 @@ def test_get_expires_at():
     assert exp_dt.tzinfo is None
     delta = datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None) - exp_dt
     assert -1 < delta.seconds < 1
+
+
+def test_is_expired():
+    # correctness not tested, but none of these should raise an exception
+    _is_expired("2024-10-01T14:26:21")
+    _is_expired("2024-10-01T14:26:21Z")
+    _is_expired(datetime.datetime.now())
+    _is_expired(datetime.datetime.now(datetime.timezone.utc))