diff --git a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/PrismContainerValueImpl.java b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/PrismContainerValueImpl.java
index bd214bf8d04..a3806e24174 100644
--- a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/PrismContainerValueImpl.java
+++ b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/PrismContainerValueImpl.java
@@ -315,7 +315,7 @@ private C asContainerableInternal(Class<C> clazz) {
 
     @NotNull
 	public Collection<QName> getItemNames() {
-	    return items.keySet();
+	    return new ArrayList<>(items.keySet());
     }
 
 	public <IV extends PrismValue,ID extends ItemDefinition> void add(Item<IV,ID> item) throws SchemaException {