diff --git a/odxtools/diaglayers/diaglayer.py b/odxtools/diaglayers/diaglayer.py
index 2f3766fc..e6884d8d 100644
--- a/odxtools/diaglayers/diaglayer.py
+++ b/odxtools/diaglayers/diaglayer.py
@@ -124,7 +124,7 @@ def _resolve_odxlinks(self, odxlinks: OdxLinkDatabase) -> None:
             # imported references only apply within this specific
             # diagnostic layer
             extended_odxlinks = copy(odxlinks)
-            extended_odxlinks.update(imported_links)
+            extended_odxlinks.update(imported_links, overwrite=False)
 
             self.diag_layer_raw._resolve_odxlinks(extended_odxlinks)
             return
diff --git a/odxtools/odxlink.py b/odxtools/odxlink.py
index 36b66ebb..259be053 100644
--- a/odxtools/odxlink.py
+++ b/odxtools/odxlink.py
@@ -230,7 +230,7 @@ def resolve_lenient(self,
 
         return None
 
-    def update(self, new_entries: Dict[OdxLinkId, Any]) -> None:
+    def update(self, new_entries: Dict[OdxLinkId, Any], *, overwrite: bool = True) -> None:
         """
         Add a bunch of new objects to the ODXLINK database.
 
@@ -244,7 +244,10 @@ def update(self, new_entries: Dict[OdxLinkId, Any]) -> None:
                 if doc_frag not in self._db:
                     self._db[doc_frag] = {}
 
-                self._db[doc_frag][odx_id.local_id] = obj
+                if overwrite:
+                    self._db[doc_frag][odx_id.local_id] = obj
+                else:
+                    self._db[doc_frag].setdefault(odx_id.local_id, obj)
 
 
 @overload