diff -r c3692364b344 -r c3df20906689 tests/run-tests.py
--- a/tests/run-tests.py	Sun Feb 25 16:14:37 2018 +0900
+++ b/tests/run-tests.py	Thu Mar 01 15:46:21 2018 -0500
@@ -1087,7 +1087,7 @@
                 del env[k]
 
         # unset env related to hooks
-        for k in env.keys():
+        for k in list(env):
             if k.startswith('HG_'):
                 del env[k]