diff --git a/scrapy/settings/__init__.py b/scrapy/settings/__init__.py
index b9a13c018..f28fbfaf9 100644
--- a/scrapy/settings/__init__.py
+++ b/scrapy/settings/__init__.py
@@ -83,7 +83,8 @@ class BaseSettings(MutableMapping):
     def __init__(self, values=None, priority='project'):
         self.frozen = False
         self.attributes = {}
-        self.update(values, priority)
+        if values is not None:
+            self.update(values, priority)
 
     def __getitem__(self, opt_name):
         if opt_name not in self: