diff --git a/meetup/api.py b/meetup/api.py
index 62983b9..01787bd 100644
--- a/meetup/api.py
+++ b/meetup/api.py
@@ -162,6 +162,8 @@ def _call(self, service_name, parameters=None, **kwargs):
             raise exceptions.HttpUnauthorized
         if response.status_code == 404:
             raise exceptions.HttpNotFoundError
+        if response.status_code == 503:
+            raise exceptions.HttpServerError
 
         # If we have two or less remaining calls in the period, wait (if the wait flag is set).
         # I tried only waiting after a 429 error, and ended getting locked out doing parallel testing.