diff --git a/Lib/test/test_support.py b/Lib/test/test_support.py
index 29a38522e0a..d6aeb29d8e4 100644
--- a/Lib/test/test_support.py
+++ b/Lib/test/test_support.py
@@ -534,7 +534,7 @@ def run_unittest(*classes):
     valid_types = (unittest.TestSuite, unittest.TestCase)
     suite = unittest.TestSuite()
     for cls in classes:
-        if isinstance(cls, str):
+        if isinstance(cls, (str, str8)):
             if cls in sys.modules:
                 suite.addTest(unittest.findTestCases(sys.modules[cls]))
             else: