diff -r 4d3557500019 Objects/setobject.c
--- a/Objects/setobject.c	Sat Jul 18 23:37:31 2015 +0300
+++ b/Objects/setobject.c	Sun Jul 19 22:19:44 2015 +0300
@@ -223,9 +223,13 @@ static int
     entry->hash = hash;
     if ((size_t)so->fill*3 < mask*2)
         return 0;
-    return set_table_resize(so, so->used);
+    if (!set_table_resize(so, so->used))
+        return 0;
+    Py_INCREF(key);
+    return -1;
 
   found_active:
+    Py_DECREF(key);
     return 0;
 }