diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index d7d77f098f6..92b7c42806b 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -569,7 +569,7 @@ class SizeofTest(unittest.TestCase):
     TPFLAGS_HEAPTYPE = 1<<9
 
     def setUp(self):
-        self.c = len(struct.pack('c', ' '))
+        self.c = len(struct.pack('c', b' '))
         self.H = len(struct.pack('H', 0))
         self.i = len(struct.pack('i', 0))
         self.l = len(struct.pack('l', 0))