diff --git a/paramiko/hostkeys.py b/paramiko/hostkeys.py
index 63b1c61..5d88084 100644
--- a/paramiko/hostkeys.py
+++ b/paramiko/hostkeys.py
@@ -162,6 +162,10 @@ class HostKeys (UserDict.DictMixin):
             raise KeyError(key)
         return ret
     
+    def __setitem__(self, key, value):
+        # don't use this please.
+        self._keys[key] = value
+    
     def keys(self):
         return self._keys.keys()