Merge branch '2.0'

1 files changed, 5 insertions, 5 deletions

diff --git a/sphinx/config.py b/sphinx/config.py
index 2bf2ae730..691cdac11 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -158,16 +158,16 @@ class Config:
 
     def __init__(self, config={}, overrides={}):
         # type: (Dict[str, Any], Dict[str, Any]) -> None
-        self.overrides = overrides
+        self.overrides = dict(overrides)
         self.values = Config.config_values.copy()
         self._raw_config = config
         self.setup = config.get('setup', None)  # type: Callable
 
-        if 'extensions' in overrides:
-            if isinstance(overrides['extensions'], str):
-                config['extensions'] = overrides.pop('extensions').split(',')
+        if 'extensions' in self.overrides:
+            if isinstance(self.overrides['extensions'], str):
+                config['extensions'] = self.overrides.pop('extensions').split(',')
             else:
-                config['extensions'] = overrides.pop('extensions')
+                config['extensions'] = self.overrides.pop('extensions')
         self.extensions = config.get('extensions', [])  # type: List[str]
 
     @classmethod