diff --git a/basyx/aas/adapter/json/json_deserialization.py b/basyx/aas/adapter/json/json_deserialization.py
index 262aebe..6524f4b 100644
--- a/basyx/aas/adapter/json/json_deserialization.py
+++ b/basyx/aas/adapter/json/json_deserialization.py
@@ -543,8 +543,8 @@ def _construct_extension(cls, dct: Dict[str, object], object_class=model.Extensi
         if 'value' in dct:
             ret.value = model.datatypes.from_xsd(_get_ts(dct, 'value', str), ret.value_type)
         if 'refersTo' in dct:
-            ret.refers_to = [cls._construct_model_reference(refers_to, model.Referable)  # type: ignore
-                             for refers_to in _get_ts(dct, 'refersTo', list)]
+            ret.refers_to = {cls._construct_model_reference(refers_to, model.Referable)  # type: ignore
+                             for refers_to in _get_ts(dct, 'refersTo', list)}
         return ret
 
     @classmethod
diff --git a/basyx/aas/adapter/xml/xml_deserialization.py b/basyx/aas/adapter/xml/xml_deserialization.py
index 76d07e1..7ae5ff7 100644
--- a/basyx/aas/adapter/xml/xml_deserialization.py
+++ b/basyx/aas/adapter/xml/xml_deserialization.py
@@ -479,9 +479,10 @@ def _amend_abstract_attributes(cls, obj: object, element: etree.Element) -> None
                                                         cls.construct_embedded_data_specification, cls.failsafe):
                     obj.embedded_data_specifications.append(eds)
         if isinstance(obj, model.HasExtension) and not cls.stripped:
-            extension_elem = element.find(NS_AAS + "extension")
+            extension_elem = element.find(NS_AAS + "extensions")
             if extension_elem is not None:
-                for extension in _failsafe_construct_multiple(extension_elem, cls.construct_extension, cls.failsafe):
+                for extension in _child_construct_multiple(extension_elem, NS_AAS + "extension",
+                                                           cls.construct_extension, cls.failsafe):
                     obj.extension.add(extension)
 
     @classmethod