diff --git a/chrome/content/zotero/elements/relatedBox.js b/chrome/content/zotero/elements/relatedBox.js
index 32827be1fa..da644d5595 100644
--- a/chrome/content/zotero/elements/relatedBox.js
+++ b/chrome/content/zotero/elements/relatedBox.js
@@ -95,7 +95,7 @@ import { getCSSItemTypeIcon } from 'components/icons';
 							+ `for item ${this._item.libraryKey}`, 2);
 					}
 					return item;
-				});
+				}).filter(Boolean);
 				
 				// Sort by display title
 				var collation = Zotero.getLocaleCollation();