diff --git a/bugsnag/utils.py b/bugsnag/utils.py
index 77b7bf8..b73b9a7 100644
--- a/bugsnag/utils.py
+++ b/bugsnag/utils.py
@@ -6,7 +6,7 @@
 import warnings
 import copy
 import logging
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from urllib.parse import urlparse, urlunsplit, parse_qs
 
 
@@ -424,7 +424,7 @@ def remove_query_from_url(url: AnyStr) -> Optional[AnyStr]:
 # fallback implementation for Python 3.5
 try:
     # this will raise if 'timespec' isn't supported
-    datetime.now(timezone.utc).isoformat(timespec='milliseconds')  # type: ignore
+    datetime.now(timezone.utc).isoformat(timespec='milliseconds')
 
     def to_rfc3339(dt: datetime) -> str:
         return dt.isoformat(timespec='milliseconds')  # type: ignore