diff --git a/s2cell/__init__.py b/s2cell/__init__.py
index 7ec298e..c635d78 100644
--- a/s2cell/__init__.py
+++ b/s2cell/__init__.py
@@ -29,11 +29,10 @@
 
 class InvalidCellID(Exception):
     """Exception type for invalid cell IDs."""
-    pass
+
 
 class InvalidToken(Exception):
     """Exception type for invalid tokens."""
-    pass
 
 
 #