diff --git a/capellambse_context_diagrams/collectors/custom.py b/capellambse_context_diagrams/collectors/custom.py
index f7ddf9f..402e685 100644
--- a/capellambse_context_diagrams/collectors/custom.py
+++ b/capellambse_context_diagrams/collectors/custom.py
@@ -198,21 +198,19 @@ def _make_box(
                 for port in getattr(obj, attr, []):
                     self._make_port_and_owner(port)
         if self.diagram._display_parent_relation:
-            current = obj
-            while (
-                current
-                and current.uuid not in self.diagram_target_owners
-                and getattr(current, "owner", None) is not None
-                and not isinstance(current.owner, generic.PackageTypes)
-            ):
-                current = self._make_owner_box(current)
-            self.common_owners.add(current.uuid)
+            owners, common_owner = generic.get_all_owner_elements(
+                obj, self.diagram_target_owners
+            )
+            for owner in owners:
+                self._make_owner_box(owner)
+            if common_owner:
+                self.common_owners.add(common_owner.uuid)
         return box
 
     def _make_owner_box(
         self,
-        obj: t.Any,
-    ) -> t.Any:
+        obj: m.ModelElement,
+    ) -> m.ModelElement:
         if not (parent_box := self.boxes.get(obj.owner.uuid)):
             parent_box = self._make_box(
                 obj.owner,
diff --git a/capellambse_context_diagrams/collectors/default.py b/capellambse_context_diagrams/collectors/default.py
index c311e0e..b534d11 100644
--- a/capellambse_context_diagrams/collectors/default.py
+++ b/capellambse_context_diagrams/collectors/default.py
@@ -256,15 +256,13 @@ def _process_ports(self) -> None:
             box.layoutOptions["portLabels.placement"] = "OUTSIDE"
 
             if self.diagram._display_parent_relation:
-                current = owner
-                while (
-                    current
-                    and current.uuid not in self.diagram_target_owners
-                    and getattr(current, "owner", None) is not None
-                    and not isinstance(current.owner, generic.PackageTypes)
-                ):
-                    current = self._make_owner_box(self.diagram, current)
-                self.common_owners.add(current.uuid)
+                owners, common_owner = generic.get_all_owner_elements(
+                    owner, self.diagram_target_owners
+                )
+                for current in owners:
+                    self._make_owner_box(self.diagram, current)
+                if common_owner:
+                    self.common_owners.add(common_owner.uuid)
 
     def _make_port(
         self, port_obj: t.Any
diff --git a/capellambse_context_diagrams/collectors/generic.py b/capellambse_context_diagrams/collectors/generic.py
index cbbe21b..be986d7 100644
--- a/capellambse_context_diagrams/collectors/generic.py
+++ b/capellambse_context_diagrams/collectors/generic.py
@@ -267,3 +267,21 @@ def get_all_owners(obj: m.ModelElement) -> cabc.Iterator[str]:
     while current is not None:
         yield current.uuid
         current = getattr(current, "owner", None)
+
+
+def get_all_owner_elements(
+    obj: m.ModelElement, excluded: list[str] | None = None
+) -> tuple[list[m.ModelElement], m.ModelElement | None]:
+    """Return a list of all owners of ``obj`` and the last owner."""
+    excluded = excluded or []
+    current: m.ModelElement | None = obj
+    owners = []
+    while (
+        current is not None
+        and current.uuid not in excluded
+        and (owner := getattr(current, "owner", None)) is not None
+        and not isinstance(current.owner, PackageTypes)
+    ):
+        owners.append(owner)
+        current = owner
+    return owners, current