diff --git a/lib/haxe/src/org/apache/thrift/helper/ObjectSet.hx b/lib/haxe/src/org/apache/thrift/helper/ObjectSet.hx
index bcf72fb..60e88e4 100644
--- a/lib/haxe/src/org/apache/thrift/helper/ObjectSet.hx
+++ b/lib/haxe/src/org/apache/thrift/helper/ObjectSet.hx
@@ -22,7 +22,7 @@
 import Map;
 
 
-class ObjectSet<K> {
+class ObjectSet<K:{}> {
 
     private var _elements = new haxe.ds.ObjectMap<K,Int>();
     private var _size : Int = 0;