diff --git a/scrapy/tests/test_utils_pqueue.py b/scrapy/tests/test_utils_pqueue.py
index 7343339ca..22f3046a8 100644
--- a/scrapy/tests/test_utils_pqueue.py
+++ b/scrapy/tests/test_utils_pqueue.py
@@ -1,19 +1,32 @@
-import unittest
+from twisted.trial import unittest
 
 from scrapy.utils.pqueue import PriorityQueue
-from scrapy.utils.queue import MemoryQueue
+from scrapy.utils.queue import MemoryQueue, DiskQueue
 
 
 class TestMemoryQueue(MemoryQueue):
 
-    def __init__(self):
-        super(TestMemoryQueue, self).__init__()
+    def __init__(self, *a, **kw):
+        super(TestMemoryQueue, self).__init__(*a, **kw)
         self.closed = False
 
     def close(self):
+        super(TestMemoryQueue, self).close()
         self.closed = True
 
-class PriorityQueueTest(unittest.TestCase):
+
+class TestDiskQueue(DiskQueue):
+
+    def __init__(self, *a, **kw):
+        super(TestDiskQueue, self).__init__(*a, **kw)
+        self.closed = False
+
+    def close(self):
+        super(TestDiskQueue, self).close()
+        self.closed = True
+
+
+class MemoryPriorityQueueTest(unittest.TestCase):
 
     def setUp(self):
         qfactory = lambda x: TestMemoryQueue()
@@ -64,6 +77,13 @@ class PriorityQueueTest(unittest.TestCase):
         self.assertEqual(sorted(self.q.close()), [1, 2, 3])
         assert all(q.closed for q in iqueues)
 
+    def test_close_return_active(self):
+        self.q.push('b', 1)
+        self.q.push('c', 2)
+        self.q.push('a', 3)
+        self.q.pop()
+        self.assertEqual(sorted(self.q.close()), [2, 3])
+
     def test_popped_internal_queues_closed(self):
         self.q.push('a', 3)
         self.q.push('b', 1)
@@ -72,3 +92,34 @@ class PriorityQueueTest(unittest.TestCase):
         self.assertEqual(self.q.pop(), 'b')
         self.q.close()
         assert p1queue.closed
+
+
+class DiskPriorityQueueTest(MemoryPriorityQueueTest):
+
+    def setUp(self):
+        qfactory = lambda x: TestDiskQueue(self.mktemp())
+        self.q = PriorityQueue(qfactory)
+
+    def test_nonserializable_object_one(self):
+        self.assertRaises(TypeError, self.q.push, lambda x: x, 0)
+        self.assertEqual(self.q.close(), [])
+
+    def test_nonserializable_object_many_close(self):
+        self.q.push('a', 3)
+        self.q.push('b', 1)
+        self.assertRaises(TypeError, self.q.push, lambda x: x, 0)
+        self.q.push('c', 2)
+        self.assertEqual(self.q.pop(), 'b')
+        self.assertEqual(sorted(self.q.close()), [2, 3])
+
+    def test_nonserializable_object_many_pop(self):
+        self.q.push('a', 3)
+        self.q.push('b', 1)
+        self.assertRaises(TypeError, self.q.push, lambda x: x, 0)
+        self.q.push('c', 2)
+        self.assertEqual(self.q.pop(), 'b')
+        self.assertEqual(self.q.pop(), 'c')
+        self.assertEqual(self.q.pop(), 'a')
+        self.assertEqual(self.q.pop(), None)
+        self.assertEqual(self.q.close(), [])
+
diff --git a/scrapy/utils/pqueue.py b/scrapy/utils/pqueue.py
index 16910239c..8ec69389d 100644
--- a/scrapy/utils/pqueue.py
+++ b/scrapy/utils/pqueue.py
@@ -20,17 +20,14 @@ class PriorityQueue(object):
         self.queues = {}
         self.qfactory = qfactory
         for p in startprios:
-            q = self.qfactory(p)
-            if q:
-                self.queues[p] = q
+            self.queues[p] = self.qfactory(p)
         self.curprio = min(startprios) if startprios else None
 
     def push(self, obj, priority=0):
-        try:
-            q = self.queues[priority]
-        except KeyError:
-            self.queues[priority] = q = self.qfactory(priority)
-        q.push(obj)
+        if priority not in self.queues:
+            self.queues[priority] = self.qfactory(priority)
+        q = self.queues[priority]
+        q.push(obj) # this may fail (eg. serialization error)
         if priority < self.curprio or self.curprio is None:
             self.curprio = priority
 
@@ -39,17 +36,20 @@ class PriorityQueue(object):
             return
         q = self.queues[self.curprio]
         m = q.pop()
-        if not q:
-            q = self.queues.pop(self.curprio)
+        if len(q) == 0:
+            del self.queues[self.curprio]
             q.close()
-            prios = self.queues.keys()
+            prios = [p for p, q in self.queues.items() if len(q) > 0]
             self.curprio = min(prios) if prios else None
         return m
 
     def close(self):
-        for q in self.queues.values():
+        active = []
+        for p, q in self.queues.items():
+            if len(q):
+                active.append(p)
             q.close()
-        return self.queues.keys()
+        return active
 
     def __len__(self):
         return sum(len(x) for x in self.queues.values()) if self.queues else 0