diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 551c3a5a4a5..9f6af7fcb69 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -882,7 +882,7 @@ class SizeofTest(unittest.TestCase):
         check = self.check_sizeof
         # _ast.AST
         import _ast
-        check(_ast.AST(), size(h + ''))
+        check(_ast.AST(), size(h + 'P'))
         # imp.NullImporter
         import imp
         check(imp.NullImporter(self.file.name), size(h + ''))