diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 0d19129..55e267f 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -420,7 +420,8 @@
 
 def _cleanup():
     for inst in _active[:]:
-        if inst.poll(_deadstate=sys.maxint) >= 0:
+        res = inst.poll(_deadstate=sys.maxint)
+        if res is not None and res >= 0:
             try:
                 _active.remove(inst)
             except ValueError: