diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -849,7 +849,7 @@ class Test(unittest.TestCase):
         env['TERM'] = 'xterm'
 
         for k in ('HG HGPROF CDPATH GREP_OPTIONS http_proxy no_proxy ' +
-                  'NO_PROXY').split():
+                  'NO_PROXY CHGDEBUG').split():
             if k in env:
                 del env[k]