diff --git a/tabellio/documents/document.py b/tabellio/documents/document.py
index 1f7f224..4bb80da 100644
--- a/tabellio/documents/document.py
+++ b/tabellio/documents/document.py
@@ -104,7 +104,7 @@ class Document(Item, BasePublication):
 
     def related_elements(self, max_items=5, closeness=0.5):
         r = BasePublication.related_elements(self, max_items, closeness)
-        doc_ids = [x.id for x in self.associated_docs]
+        doc_ids = [x.id for x in (self.associated_docs or [])]
         return [x for x in r if ((type(x.getId) is str) and x.getId or x.getId()) not in doc_ids]
 
     @property