diff --git a/src/cco-extensions/ModalRelationOntology.ttl b/src/cco-extensions/ModalRelationOntology.ttl
index caf986c..1651d30 100644
--- a/src/cco-extensions/ModalRelationOntology.ttl
+++ b/src/cco-extensions/ModalRelationOntology.ttl
@@ -1578,7 +1578,7 @@ mro:ont00001861 rdf:type owl:ObjectProperty ;
                 rdfs:domain obo:BFO_0000030 ;
                 rdfs:range obo:BFO_0000030 ;
                 rdfs:label "is material of"@en ;
-                <http://www.w3.org/2004/02/skos/core#definition> "An object m is material of an object o when m is the material of which o consists and that material does not undergo a change of kind during the creation of o"@en ;
+                <http://www.w3.org/2004/02/skos/core#definition> "x is_material_of y when both x and y are instances of Object and x is the material that y consists of and which undergoes no change of kind during the creation of y."@en ;
                 cco:ont00001760 <https://www.commoncoreontologies.org/ModalRelationOntology> .