diff --git a/plexapi/myplex.py b/plexapi/myplex.py
index ec8a85a04..4b920b828 100644
--- a/plexapi/myplex.py
+++ b/plexapi/myplex.py
@@ -565,7 +565,7 @@ def _filterDictToStr(self, filterDict):
         """ Converts friend filters to a string representation for transport. """
         values = []
         for key, vals in filterDict.items():
-            if key not in ('contentRating', 'label'):
+            if key not in ('contentRating', 'label', 'contentRating!', 'label!'):
                 raise BadRequest('Unknown filter key: %s', key)
             values.append('%s=%s' % (key, '%2C'.join(vals)))
         return '|'.join(values)