diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 1544ff369d0..c49ee4a6cc6 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -511,7 +511,7 @@ class PythonLanguage(object):
         config.run,
         timeout_seconds=5*60,
         environ=dict(list(environment.items()) +
-                     [('GRPC_PYTHON_TESTRUNNER_FILTER', suite_name)]),
+                     [('GRPC_PYTHON_TESTRUNNER_FILTER', str(suite_name))]),
         shortname='%s.test.%s' % (config.name, suite_name),)
         for suite_name in tests_json
         for config in self.pythons]