diff --git a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
index 5899319..1aa0d8f 100644
--- a/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
+++ b/src/main/java/eu/dnetlib/dhp/schema/common/ModelSupport.java
@@ -163,7 +163,7 @@ public class ModelSupport {
 	 * @param encoding
 	 * @return the relation inverse descriptor, throws @IllegalArgumentException when not found.
 	 */
-	public RelationInverse findInverse(String encoding) {
+	public static RelationInverse findInverse(String encoding) {
 		return ModelSupport.relationInverseMap
 				.entrySet()
 				.stream()