diff --git a/server.py b/server.py
index 9381b59..b170483 100644
--- a/server.py
+++ b/server.py
@@ -2814,8 +2814,9 @@ async def verify_invitation_token(
     if not invitation:
         raise HTTPException(status_code=404, detail="Invalid or expired invitation token")
 
-    # Check expiry
-    if invitation.expires_at < datetime.now(timezone.utc):
+    # Check expiry (handle timezone-naive datetime from DB)
+    expires_at_aware = invitation.expires_at.replace(tzinfo=timezone.utc) if invitation.expires_at.tzinfo is None else invitation.expires_at
+    if expires_at_aware < datetime.now(timezone.utc):
         invitation.status = InvitationStatus.expired
         db.commit()
         raise HTTPException(status_code=400, detail="Invitation has expired")
@@ -2847,8 +2848,9 @@ async def accept_invitation(
     if not invitation:
         raise HTTPException(status_code=404, detail="Invalid or expired invitation token")
 
-    # Check expiry
-    if invitation.expires_at < datetime.now(timezone.utc):
+    # Check expiry (handle timezone-naive datetime from DB)
+    expires_at_aware = invitation.expires_at.replace(tzinfo=timezone.utc) if invitation.expires_at.tzinfo is None else invitation.expires_at
+    if expires_at_aware < datetime.now(timezone.utc):
         invitation.status = InvitationStatus.expired
         db.commit()
         raise HTTPException(status_code=400, detail="Invitation has expired")