diff --git a/lib/sequence/weakrefset.rb b/lib/sequence/weakrefset.rb
index 5b6723a..4dcd26b 100755
--- a/lib/sequence/weakrefset.rb
+++ b/lib/sequence/weakrefset.rb
@@ -113,7 +113,9 @@ def == other
   alias eql? ==
 
   def hash
-      to_a.hash
+    result=0
+    each{|x| result^=x.hash }
+    result
   end
     
   # clear the set (return self)