diff --git a/djgeojson/serializers.py b/djgeojson/serializers.py
index f27c83b..ba32fd8 100644
--- a/djgeojson/serializers.py
+++ b/djgeojson/serializers.py
@@ -264,7 +264,7 @@ def serialize_values_queryset(self, queryset):
             self.handle_field(obj, self.geometry_field)
 
             for field_name in obj:
-                if not field_name in obj:
+                if field_name not in obj:
                     continue
                 if self.properties is None or field_name in self.properties:
                     self.handle_field(obj, field_name)