diff --git a/src/blenderbim/blenderbim/bim/module/aggregate/operator.py b/src/blenderbim/blenderbim/bim/module/aggregate/operator.py
index bf336ad69b..146ab4579b 100644
--- a/src/blenderbim/blenderbim/bim/module/aggregate/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/aggregate/operator.py
@@ -44,7 +44,12 @@ class BIM_OT_aggregate_assign_object(bpy.types.Operator, Operator):
     def _execute(self, context):
         relating_obj = None
         if self.relating_object:
-            relating_obj = tool.Ifc.get_object(tool.Ifc.get().by_id(self.relating_object))
+            element = tool.Ifc.get().by_id(self.relating_object)
+            if element.IsDecomposedBy:
+                relating_obj = tool.Ifc.get_object(tool.Ifc.get().by_id(self.relating_object))
+            else:
+                assembly = element.Decomposes[0].RelatingObject
+                relating_obj = tool.Ifc.get_object(assembly)
         elif context.active_object:
             relating_obj = context.active_object
         if not relating_obj: