diff --git a/src/ifcopenshell-python/ifcopenshell/api/project/append_asset.py b/src/ifcopenshell-python/ifcopenshell/api/project/append_asset.py
index 79eb418099..c5b4808f98 100644
--- a/src/ifcopenshell-python/ifcopenshell/api/project/append_asset.py
+++ b/src/ifcopenshell-python/ifcopenshell/api/project/append_asset.py
@@ -206,14 +206,17 @@ class Usecase:
             self.target_class = "IfcPresentationStyle"
             return self.append_presentation_style()
 
+    def by_guid(self, guid: str) -> Union[ifcopenshell.entity_instance, None]:
+        try:
+            return self.file.by_guid(guid)
+        except RuntimeError:
+            return None
+
     def get_existing_element(self, element: ifcopenshell.entity_instance) -> Union[ifcopenshell.entity_instance, None]:
         if element.id() in self.added_elements:
             return self.added_elements[element.id()]
         if element.is_a("IfcRoot"):
-            try:
-                return self.file.by_guid(element.GlobalId)
-            except RuntimeError:
-                return None
+            return self.by_guid(element.GlobalId)
         elif not self.assume_asset_uniqueness_by_name:
             return None
         elif element.is_a("IfcMaterial"):
@@ -364,10 +367,13 @@ class Usecase:
         # Check if inverse element was created before.
         # Still need to recreate it again - e.g. it could be some rel
         # that now needs it's RelatingObjects to be extended by the current asset.
+        existing_rel = None
         if (new := self.reuse_identities.get(element_identity)) is not None:
             # Currently known cases requiring attributes reassignment are rels.
             if not new.is_a("IfcRelationship"):
                 return
+        elif element.is_a("IfcRelationship") and (existing_rel := self.by_guid(element.GlobalId)):
+            new = existing_rel
         else:
             new = self.file.create_entity(element.is_a())
             self.reuse_identities[element_identity] = new
@@ -382,6 +388,11 @@ class Usecase:
                 for item in attribute:
                     if not self.is_another_asset(item):
                         new_attribute.append(self.add_element(item))
+                # If rel exists we need to make sure previously assigned elements are untouched
+                # e.g. not to assign a material or a pset from element.
+                if existing_rel:
+                    new_attribute.extend(existing_rel[i])
+                    new_attribute = list(set(new_attribute))
             else:
                 new_attribute = attribute
             if new_attribute is not None:
@@ -389,19 +400,12 @@ class Usecase:
 
     def is_another_asset(self, element: ifcopenshell.entity_instance) -> bool:
         """Is IFC entity from inverse attribute is another asset to append that should be skipped."""
-
-        def by_guid(guid: str) -> Union[ifcopenshell.entity_instance, None]:
-            try:
-                return self.file.by_guid(guid)
-            except RuntimeError:
-                return None
-
         if element == self.settings["element"]:
             return False
         elif element.is_a("IfcFeatureElement"):
             # Feature elements match the target class but aren't considered "assets"
             return False
-        elif element.is_a("IfcRoot") and by_guid(element.GlobalId) is not None:
+        elif element.is_a("IfcRoot") and self.by_guid(element.GlobalId) is not None:
             return False
         elif element.is_a(self.target_class):
             return True
diff --git a/src/ifcopenshell-python/test/api/project/test_append_asset.py b/src/ifcopenshell-python/test/api/project/test_append_asset.py
index 30f4322199..cee115df4c 100644
--- a/src/ifcopenshell-python/test/api/project/test_append_asset.py
+++ b/src/ifcopenshell-python/test/api/project/test_append_asset.py
@@ -459,6 +459,24 @@ class TestAppendAssetIFC2X3(test.bootstrap.IFC2X3):
         assert "Test" in pset_data
         assert ifcopenshell.util.element.get_psets(element2_) == pset_data
 
+    def test_update_rels_appending_subsequent_assets_identifying_rels_by_guids(self):
+        library = ifcopenshell.api.project.create_file(version=self.file.schema)
+        element1 = ifcopenshell.api.root.create_entity(library, ifc_class="IfcWall")
+        pset = ifcopenshell.api.pset.add_pset(library, product=element1, name="Test")
+        element2 = ifcopenshell.api.root.create_entity(library, ifc_class="IfcWall")
+        pset_rel = ifcopenshell.api.pset.assign_pset(library, pset=pset, products=[element2])
+        assert pset_rel
+        pset_rel_guid: str = pset_rel.GlobalId
+
+        element1_ = ifcopenshell.api.project.append_asset(self.file, library, element1)
+        element2_ = ifcopenshell.api.project.append_asset(self.file, library, element2)
+        pset_data = ifcopenshell.util.element.get_psets(element1_)
+
+        appended_rels = [e for e in self.file.by_type("IfcRelDefinesByProperties") if e.GlobalId == pset_rel_guid]
+        assert len(appended_rels) == 1
+        assert set(appended_rels[0].RelatedObjects) == {element1_, element2_}
+        assert ifcopenshell.util.element.get_psets(element2_) == pset_data
+
     def test_reuse_identities_to_avoid_removed_entities_and_possible_crashes(self):
         self.file.create_entity("IfcProject")
         context = ifcopenshell.api.context.add_context(self.file, context_type="Model")