diff --git a/model_utils/models.py b/model_utils/models.py
index 26cec0b..6083015 100644
--- a/model_utils/models.py
+++ b/model_utils/models.py
@@ -196,7 +196,7 @@ class SaveSignalHandlingModel(models.Model):
         if cls._meta.proxy:
             cls = cls._meta.concrete_model
         meta = cls._meta
-        if not meta.auto_created and not 'pre_save' in self.signals_to_disable:
+        if not meta.auto_created and 'pre_save' not in self.signals_to_disable:
             pre_save.send(
                 sender=origin, instance=self, raw=raw, using=using,
                 update_fields=update_fields,
@@ -209,7 +209,7 @@ class SaveSignalHandlingModel(models.Model):
         self._state.db = using
         self._state.adding = False
 
-        if not meta.auto_created and not 'post_save' in self.signals_to_disable:
+        if not meta.auto_created and 'post_save' not in self.signals_to_disable:
             post_save.send(
                 sender=origin, instance=self, created=(not updated),
                 update_fields=update_fields, raw=raw, using=using,