diff --git a/scrapy/utils/datatypes.py b/scrapy/utils/datatypes.py
index fbc41f760..231234e3d 100644
--- a/scrapy/utils/datatypes.py
+++ b/scrapy/utils/datatypes.py
@@ -245,7 +245,7 @@ class MergeDict(object):
     first occurrence will be used.
     """
     def __init__(self, *dicts):
-        if six.PY3:
+        if not six.PY2:
             warnings.warn(
                 "scrapy.utils.datatypes.MergeDict is deprecated in favor "
                 "of collections.ChainMap (introduced in Python 3.3)",