diff --git a/sdk/basyx/aas/model/base.py b/sdk/basyx/aas/model/base.py
index 35ccad5a..edb1c302 100644
--- a/sdk/basyx/aas/model/base.py
+++ b/sdk/basyx/aas/model/base.py
@@ -10,6 +10,7 @@
 """
 
 import abc
+from datetime import datetime
 import inspect
 import itertools
 from enum import Enum, unique
@@ -26,6 +27,7 @@
 ValueDataType = datatypes.AnyXSDType  # any xsd atomic type (from .datatypes)
 ValueList = Set["ValueReferencePair"]
 BlobType = bytes
+DateTimeUTC = datetime
 
 # The following string aliases are constrained by the decorator functions defined in the string_constraints module,
 # wherever they are used for an instance attributes.
diff --git a/sdk/basyx/aas/model/submodel.py b/sdk/basyx/aas/model/submodel.py
index 9e7321c4..86556c37 100644
--- a/sdk/basyx/aas/model/submodel.py
+++ b/sdk/basyx/aas/model/submodel.py
@@ -10,6 +10,7 @@
 
 import abc
 import uuid
+from datetime import timezone
 from typing import Optional, Set, Iterable, TYPE_CHECKING, List, Type, TypeVar, Generic, Union
 
 from . import base, datatypes, _string_constraints
@@ -1284,7 +1285,7 @@ def __init__(self,
                  message_topic: Optional[base.MessageTopicType] = None,
                  message_broker: Optional[base.ModelReference[Union[Submodel, SubmodelElementList,
                                                                     SubmodelElementCollection, Entity]]] = None,
-                 last_update: Optional[datatypes.DateTime] = None,
+                 last_update: Optional[base.DateTimeUTC] = None,
                  min_interval: Optional[datatypes.Duration] = None,
                  max_interval: Optional[datatypes.Duration] = None,
                  display_name: Optional[base.MultiLanguageNameType] = None,
@@ -1310,7 +1311,11 @@ def __init__(self,
         self.message_topic: Optional[base.MessageTopicType] = message_topic
         self.message_broker: Optional[base.ModelReference[Union[Submodel, SubmodelElementList,
                                                                 SubmodelElementCollection, Entity]]] = message_broker
-        self.last_update: Optional[datatypes.DateTime] = last_update
+        self.last_update: Optional[base.DateTimeUTC] = last_update
+        if ((last_update and last_update.tzinfo and
+                last_update.tzinfo.utcoffset(last_update) != timezone.utc.utcoffset(None))
+                or (last_update and last_update.tzinfo is None)):
+            raise ValueError("Last update must be in UTC!")
         self.min_interval: Optional[datatypes.Duration] = min_interval
         self.max_interval: Optional[datatypes.Duration] = max_interval