--- a/tests/run-tests.py	Thu Apr 14 15:26:18 2016 -0400
+++ b/tests/run-tests.py	Wed Apr 13 13:51:39 2016 +0000
@@ -2115,6 +2115,7 @@
 
         if self.options.pure:
             os.environ["HGTEST_RUN_TESTS_PURE"] = "--pure"
+            os.environ["HGMODULEPOLICY"] = "py"
 
         if self.options.allow_slow_tests:
             os.environ["HGTEST_SLOW"] = "slow"