diff --git a/kademlia/node.py b/kademlia/node.py
index 6d90493..5f82c29 100644
--- a/kademlia/node.py
+++ b/kademlia/node.py
@@ -94,8 +94,9 @@ class NodeHeap(object):
             nodes = [nodes]
 
         for node in nodes:
-            distance = self.node.distanceTo(node)
-            heapq.heappush(self.heap, (distance, node))
+	    if node not in self:
+                distance = self.node.distanceTo(node)
+                heapq.heappush(self.heap, (distance, node))
 
     def __len__(self):
         return min(len(self.heap), self.maxsize)
@@ -104,5 +105,11 @@ class NodeHeap(object):
         nodes = heapq.nsmallest(self.maxsize, self.heap)
         return iter(map(itemgetter(1), nodes))
 
+    def __contains__(self, node):
+        for distance, n in self.heap:
+            if node.id == n.id:
+                return True
+        return False	
+
     def getUncontacted(self):
         return [n for n in self if n.id not in self.contacted]