diff --git a/test/test_library.py b/test/test_library.py
index 0bac0f173..3515c855c 100644
--- a/test/test_library.py
+++ b/test/test_library.py
@@ -1007,8 +1007,8 @@ class PathStringTest(_common.TestCase):
 class PathTruncationTest(_common.TestCase):
     def test_truncate_bytestring(self):
         with _common.platform_posix():
-            p = util.truncate_path('abcde/fgh', 4)
-        self.assertEqual(p, 'abcd/fgh')
+            p = util.truncate_path(b'abcde/fgh', 4)
+        self.assertEqual(p, b'abcd/fgh')
 
     def test_truncate_unicode(self):
         with _common.platform_posix():