diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 0dd4258..d9b3267 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -769,6 +769,11 @@ class SizeofTest(unittest.TestCase):
                   '10P'                 # PySequenceMethods
                   '6P'                  # PyBufferProcs
                   '2P')
+
+        # COUNT_ALLOCS adds further fields to the end of a PyTypeObject:
+        if hasattr(sys, 'getcounts'):
+            s += size('P')
+
         class newstyleclass(object):
             pass
         check(newstyleclass, s)