diff --git a/setuptools/command/build_py.py b/setuptools/command/build_py.py
index 758a3fdfe8c..1b0daff728f 100644
--- a/setuptools/command/build_py.py
+++ b/setuptools/command/build_py.py
@@ -8,6 +8,7 @@
 import distutils.errors
 import itertools
 
+from setuptools.extern.six import string_types
 from setuptools.extern.six.moves import map, filter, filterfalse
 
 try:
@@ -66,6 +67,10 @@ def __getattr__(self, attr):
         return orig.build_py.__getattr__(self, attr)
 
     def build_module(self, module, module_file, package):
+        # Ensure that package names are strings in case an ancient distutils
+        # library is called
+        if isinstance(package, string_types):
+            package = str(package)
         outfile, copied = orig.build_py.build_module(self, module, module_file,
                                                      package)
         if copied: