diff --git a/funidata_utils/schemas/sisu/course_unit_realisation.py b/funidata_utils/schemas/sisu/course_unit_realisation.py
index 0f2f38e..90e5985 100644
--- a/funidata_utils/schemas/sisu/course_unit_realisation.py
+++ b/funidata_utils/schemas/sisu/course_unit_realisation.py
@@ -124,11 +124,16 @@ class CourseUnitRealisation(SisBase):
     cooperationNetworkDetails: CooperationNetworkDetails | None = None
     copyDetails: CopyDetails | None = None
 
-    @field_serializer("assessmentItemIds", "literature", "learningEnvironments")
+    @field_serializer("literature", "learningEnvironments")
     def serialize_set_as_list(self, v, _info) -> list[dict] | None:
         serialized_list = serialize_as_list(v)
         return serialized_list
 
+    @field_serializer("assessmentItemIds")
+    def serialize_set_as_list_str(self, v, _info) -> list[str] | None:
+        serialized_list = serialize_as_list(v)
+        return serialized_list
+
     @field_serializer('lateEnrolmentEnd', 'enrolmentAdditionalCancellationEnd', 'confirmedStudySubGroupModificationEnd')
     def serialize_date_time_as_str(self, dt: datetime | None, _info):
         if dt is None: