diff --git a/sphinx/environment/__init__.py b/sphinx/environment/__init__.py
index fc5ac691a..c04073163 100644
--- a/sphinx/environment/__init__.py
+++ b/sphinx/environment/__init__.py
@@ -67,6 +67,7 @@ default_settings = {
     'sectsubtitle_xform': False,
     'halt_level': 5,
     'file_insertion_enabled': True,
+    'smartquotes_locales': [],
 }
 
 # This is increased every time an environment attribute is added