--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -346,8 +346,9 @@ DAEMON_PIDS = os.environ["DAEMON_PIDS"]
HGRCPATH = os.environ["HGRCPATH"] = os.path.join(HGTMP, '.hgrc')
os.environ["HGEDITOR"] = sys.executable + ' -c "import sys; sys.exit(0)"'
-os.environ["HGMERGE"] = 'python "%s"' % os.path.join(TESTDIR, os.path.pardir,
- 'contrib', 'simplemerge')
+os.environ["HGMERGE"] = ('python "%s" -L my -L other'
+ % os.path.join(TESTDIR, os.path.pardir, 'contrib',
+ 'simplemerge'))
os.environ["HGUSER"] = "test"
os.environ["HGENCODING"] = "ascii"
os.environ["HGENCODINGMODE"] = "strict"