diff --git a/apitools/base/py/encoding.py b/apitools/base/py/encoding.py
index 7eec985d..182f1666 100644
--- a/apitools/base/py/encoding.py
+++ b/apitools/base/py/encoding.py
@@ -230,8 +230,7 @@ def _GetField(message, field_path):
 
 def _SetField(dictblob, field_path, value):
     for field in field_path[:-1]:
-        dictblob[field] = {}
-        dictblob = dictblob[field]
+        dictblob = dictblob.setdefault(field, {})
     dictblob[field_path[-1]] = value
 
 
diff --git a/apitools/base/py/encoding_test.py b/apitools/base/py/encoding_test.py
index d306aaed..3564ca04 100644
--- a/apitools/base/py/encoding_test.py
+++ b/apitools/base/py/encoding_test.py
@@ -203,9 +203,12 @@ def testNestedIncludeFields(self):
         self.assertEqual(
             '{"nested": {"nested": null}}',
             encoding.MessageToJson(msg, include_fields=['nested.nested']))
-        self.assertEqual(
-            '{"nested": {"nested_list": []}}',
-            encoding.MessageToJson(msg, include_fields=['nested.nested_list']))
+        # When clearing 'nested.nested_list', its sibling ('nested.nested')
+        # should remain unaffected.
+        self.assertIn(
+            encoding.MessageToJson(msg, include_fields=['nested.nested_list']),
+            ['{"nested": {"nested": {}, "nested_list": []}}',
+             '{"nested": {"nested_list": [], "nested": {}}}'])
         self.assertEqual(
             '{"nested": {"nested": {"additional_properties": []}}}',
             encoding.MessageToJson(