diff --git a/Application/src/eurocontrol/swim/model/rules/aixm/mapping/AIXM51_Features_MappingRule.java b/Application/src/eurocontrol/swim/model/rules/aixm/mapping/AIXM51_Features_MappingRule.java
index a3859f9..36806bf 100644
--- a/Application/src/eurocontrol/swim/model/rules/aixm/mapping/AIXM51_Features_MappingRule.java
+++ b/Application/src/eurocontrol/swim/model/rules/aixm/mapping/AIXM51_Features_MappingRule.java
@@ -515,7 +515,7 @@ protected org.w3c.dom.Element createFeatureType(Element feature)
 	        {
 	            extensionBaseName = umlParent.GetName() + "Type";
 	        }
-	        extension.setAttribute("base", getNamespacePrefixForElement(feature) + ":" + extensionBaseName);
+	        extension.setAttribute("base", getNamespacePrefixForElement(umlParent) + ":" + extensionBaseName);
 	    }
 	    else
 	    {