diff --git a/requirements.txt b/requirements.txt
index b8e2e51..2a0c119 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,2 @@
 argparse
-six>=1.5.2
+six>=1.6.0
diff --git a/setup.py b/setup.py
index 70c2b3f..7363757 100644
--- a/setup.py
+++ b/setup.py
@@ -17,6 +17,14 @@
 # THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
+# In python < 2.7.4, a lazy loading of package `pbr` will break
+# setuptools if some other modules registered functions in `atexit`.
+# solution from: http://bugs.python.org/issue15881#msg170215
+try:
+    import multiprocessing  # noqa
+except ImportError:
+    pass
+
 setuptools.setup(
     setup_requires=['pbr'],
     pbr=True)