diff --git a/sourcefinder/utility/containers.py b/sourcefinder/utility/containers.py
index c1d43e2..46bf2a0 100644
--- a/sourcefinder/utility/containers.py
+++ b/sourcefinder/utility/containers.py
@@ -52,12 +52,6 @@ def __setslice__(self, section, items):
         """
         raise NotImplementedError
 
-    def __iadd__(self, y):
-        """
-        Not implemented.
-        """
-        raise NotImplementedError
-
     def __imul__(self, y):
         """
         Not implemented.