diff --git a/docs/writing/structure.rst b/docs/writing/structure.rst
index b06e15a..b33d6f6 100644
--- a/docs/writing/structure.rst
+++ b/docs/writing/structure.rst
@@ -633,7 +633,7 @@ with the class approach:
 
     class CustomOpen(object):
         def __init__(self, filename):
-          self.file = open(filename)
+            self.file = open(filename)
 
         def __enter__(self):
             return self.file