diff --git a/lemur/certificates/models.py b/lemur/certificates/models.py
index 2ca88b00..9d7a459c 100644
--- a/lemur/certificates/models.py
+++ b/lemur/certificates/models.py
@@ -8,6 +8,8 @@
 from datetime import timedelta
 
 import arrow
+import pytz
+import datetime
 from cryptography import x509
 from cryptography.hazmat.primitives.asymmetric import rsa
 from flask import current_app
@@ -321,8 +323,13 @@ class Certificate(db.Model):
 
     @hybrid_property
     def expired(self):
-        if self.not_after <= arrow.utcnow():
-            return True
+        if isinstance(self.not_after, datetime.datetime):
+            # can't compare offset-naive and offset-aware datetimes
+            if self.not_after.replace(tzinfo=pytz.UTC) <= arrow.utcnow():
+                return True
+        else:
+            if self.not_after <= arrow.utcnow():
+                return True
 
     @expired.expression
     def expired(cls):