Distutils apparently requires an absolute path so provide one.
diff --git a/setup.py b/setup.py
index ff37bc4..4599927 100644
--- a/setup.py
+++ b/setup.py
@@ -117,7 +117,7 @@
         if not srcdir:
             # Maybe running on Windows but not using CYGWIN?
             raise ValueError("No source directory; cannot proceed.")
-        srcdir = os.path.normpath(srcdir)
+        srcdir = os.path.abspath(srcdir)
         moddirlist = [os.path.join(srcdir, 'Modules')]
 
         # Platform-dependent module source and include directories