diff --git a/Lib/site.py b/Lib/site.py
index 06185502481..d6e915239ad 100644
--- a/Lib/site.py
+++ b/Lib/site.py
@@ -102,6 +102,8 @@ def addbuilddir():
     (especially for Guido :-)"""
     from distutils.util import get_platform
     s = "build/lib.%s-%.3s" % (get_platform(), sys.version)
+    if hasattr(sys, 'gettotalrefcount'):
+        s += '-pydebug'
     s = os.path.join(os.path.dirname(sys.path[-1]), s)
     sys.path.append(s)