diff --git a/scrapy/core/scheduler.py b/scrapy/core/scheduler.py
index 2b167a6dc..0a2a15b48 100644
--- a/scrapy/core/scheduler.py
+++ b/scrapy/core/scheduler.py
@@ -58,7 +58,7 @@ class Scheduler(object):
         return dfd
 
     def clear_pending_requests(self, spider):
-        pass
+        self.pending_requests[spider].clear()
 
     def next_request(self, spider):
         """Return the next available request to be downloaded for a spider.
diff --git a/scrapy/utils/datatypes.py b/scrapy/utils/datatypes.py
index 044bcae27..621934657 100644
--- a/scrapy/utils/datatypes.py
+++ b/scrapy/utils/datatypes.py
@@ -305,6 +305,11 @@ class PriorityQueue(object):
                         del self.positems[priority]
                     return t
         raise IndexError("pop from an empty queue")
+    
+    def clear(self):
+        self.negitems.clear()
+        self.pzero.clear()
+        self.positems.clear()
 
     def __len__(self):
         total = sum(len(v) for v in self.negitems.values()) + \