diff --git a/bson/son.py b/bson/son.py
index dd4ba979f..520cdd263 100644
--- a/bson/son.py
+++ b/bson/son.py
@@ -124,14 +124,20 @@ class SON(dict):
     # efficient.
     # second level definitions support higher levels
     def __iter__(self):
-        for k in self.keys():
+        """
+        Cannot remove nor add keys while iterating
+        """
+        key_len = len(self.__keys)
+        for k in self.__keys:
+            if len(self.__keys) != key_len:
+                raise RuntimeError("son changed length during iteration")
             yield k
 
     def has_key(self, key):
-        return key in self.keys()
+        return key in self.__keys
 
     def __contains__(self, key):
-        return key in self.keys()
+        return key in self.__keys
 
     # third level takes advantage of second level definitions
     def iteritems(self):
@@ -153,8 +159,8 @@ class SON(dict):
         return [(key, self[key]) for key in self]
 
     def clear(self):
-        for key in self.keys():
-            del self[key]
+        self.__keys = []
+        super(SON, self).clear()
 
     def setdefault(self, key, default=None):
         try:
diff --git a/doc/contributors.rst b/doc/contributors.rst
index 3488fc8cd..5c1ec55b0 100644
--- a/doc/contributors.rst
+++ b/doc/contributors.rst
@@ -70,3 +70,4 @@ The following is a list of people who have contributed to
 - Kyle Erf (3rf)
 - Luke Lovett (lovett89)
 - Jaroslav Semančík (girogiro)
+- Don Mitchell (dmitchell)
diff --git a/test/test_son.py b/test/test_son.py
index 02312ac59..8e101e97e 100644
--- a/test/test_son.py
+++ b/test/test_son.py
@@ -154,6 +154,52 @@ class TestSON(unittest.TestCase):
         self.assertEqual(list(reflexive_son), list(reflexive_son1))
         self.assertEqual(id(reflexive_son1), id(reflexive_son1["reflexive"]))
 
+    def test_iteration(self):
+        """
+        Test __iter__
+        """
+        # test success case
+        test_son = SON([(1, 100), (2, 200), (3, 300)])
+        for ele in test_son:
+            self.assertEqual(ele * 100, test_son[ele])
+        # test failure case
+        def break_iter():
+            for ele in test_son:
+                del test_son[ele]
+        self.assertRaises(RuntimeError, break_iter)
+
+    def test_contains_has(self):
+        """
+        has_key and __contains__
+        """
+        test_son = SON([(1, 100), (2, 200), (3, 300)])
+        self.assertIn(1, test_son)
+        self.assertTrue(2 in test_son, "in failed")
+        self.assertFalse(22 in test_son, "in succeeded when it shouldn't")
+        self.assertTrue(test_son.has_key(2), "has_key failed")
+        self.assertFalse(test_son.has_key(22), "has_key succeeded when it shouldn't")
+
+    def test_clears(self):
+        """
+        Test clear()
+        """
+        test_son = SON([(1, 100), (2, 200), (3, 300)])
+        test_son.clear()
+        self.assertNotIn(1, test_son)
+        self.assertEqual(0, len(test_son))
+        self.assertEqual(0, len(test_son.keys()))
+        self.assertEqual({}, test_son.to_dict())
+
+    def test_len(self):
+        """
+        Test len
+        """
+        test_son = SON()
+        self.assertEqual(0, len(test_son))
+        test_son = SON([(1, 100), (2, 200), (3, 300)])
+        self.assertEqual(3, len(test_son))
+        test_son.popitem()
+        self.assertEqual(2, len(test_son))
 
 if __name__ == "__main__":
     unittest.main()