diff --git a/run_tests b/run_tests
index d7144b3c..a09ab382 100755
--- a/run_tests
+++ b/run_tests
@@ -42,9 +42,11 @@ def main(argv):
   """The main entry."""
   # Add the repo tree to PYTHONPATH as the tests expect to be able to import
   # modules directly.
-  topdir = os.path.dirname(os.path.realpath(__file__))
-  pythonpath = os.environ.get('PYTHONPATH', '')
-  os.environ['PYTHONPATH'] = '%s:%s' % (topdir, pythonpath)
+  pythonpath = os.path.dirname(os.path.realpath(__file__))
+  oldpythonpath = os.environ.get('PYTHONPATH', None)
+  if oldpythonpath is not None:
+    pythonpath += os.pathsep + oldpythonpath
+  os.environ['PYTHONPATH'] = pythonpath
 
   return run_pytest('pytest', argv)
 
diff --git a/tox.ini b/tox.ini
index bd1e18cc..1a9642a3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -19,7 +19,11 @@ envlist = py27, py36, py37, py38
 
 [testenv]
 deps = pytest
-commands = {toxinidir}/run_tests
+commands = {envpython} run_tests
+setenv =
+    GIT_AUTHOR_NAME = Repo test author
+    GIT_COMMITTER_NAME = Repo test committer
+    EMAIL = repo@gerrit.nodomain
 
 [testenv:py27]
 deps =