X-Git-Url: http://nitlanguage.org

diff --git a/src/metamodel/partial_order.nit b/src/metamodel/partial_order.nit
index 9fe3ba3..435e3d9 100644
--- a/src/metamodel/partial_order.nit
+++ b/src/metamodel/partial_order.nit
@@ -19,8 +19,8 @@ package partial_order
 
 # Handles partial ordered sets (ie hierarchies)
 # Thez are built by adding new element at the bottom of the hierarchy
-class PartialOrder[E]
-special Collection[E]
+class PartialOrder[E: Object]
+	super Collection[E]
 	# Elements
 	var _elements: Map[E, PartialOrderElement[E]]
 
@@ -186,7 +186,7 @@ special Collection[E]
 	end
 end
 
-class PartialOrderElement[E]
+class PartialOrderElement[E: Object]
 	# The partial order where belong self
 	readable var _order: PartialOrder[E]