--- bin/pd-nagios.orig	2017-10-05 18:21:38 UTC
+++ bin/pd-nagios
@@ -101,7 +101,7 @@ class NagiosEvent:
         if not NagiosEvent.REQUIRED_FIELDS[self._notification_type].issubset(self._details.keys()):
             msg = "Missing fields for type '{0}'.  {1} required".format(
                 self._notification_type,
-                ", ".join(self._required_fields())
+                ", ".join(NagiosEvent.REQUIRED_FIELDS[self._notification_type])
                 )
             raise ValueError(msg)