diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index f3b0d1d470..1e7f64709f 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,10 @@ in development
 Added
 ~~~~~
 
+* Enable setting ttl for MockDatastoreService. #5468
+
+  Contributed by @ytjohn
+
 * Added st2 API and CLI command for actions clone operation.
 
   API endpoint ``/api/v1/actions/{ref_or_id}/clone`` takes ``ref_or_id`` of source action.
diff --git a/st2tests/st2tests/mocks/datastore.py b/st2tests/st2tests/mocks/datastore.py
index 0282a18ffd..e1adcde153 100644
--- a/st2tests/st2tests/mocks/datastore.py
+++ b/st2tests/st2tests/mocks/datastore.py
@@ -34,6 +34,7 @@ def __init__(self, logger, pack_name, class_name, api_username=None):
         self._pack_name = pack_name
         self._class_name = class_name
         self._username = api_username or "admin"
+        self._logger = logger
 
         # Holds mock KeyValuePair objects
         # Key is a KeyValuePair name and value is the KeyValuePair object
@@ -96,10 +97,6 @@ def set_value(
         """
         Store a value in a dictionary which is local to this class.
         """
-        if ttl:
-            raise ValueError(
-                'MockDatastoreService.set_value doesn\'t support "ttl" argument'
-            )
 
         name = self._get_full_key_name(name=name, local=local)
 
@@ -107,6 +104,11 @@ def set_value(
         instance.id = name
         instance.name = name
         instance.value = value
+        if ttl:
+            self._logger.warning(
+                "MockDatastoreService is not able to expire keys based on ttl."
+            )
+            instance.ttl = ttl
 
         self._datastore_items[name] = instance
         return True