diff --git a/model/Items.inc.php b/model/Items.inc.php
index df08d0c6..6caf5de6 100644
--- a/model/Items.inc.php
+++ b/model/Items.inc.php
@@ -1697,7 +1697,9 @@ public static function updateFromJSON(Zotero_Item $item,
 					continue 2;
 				
 				case 'parentItem':
-					$item->setSourceKey($val);
+					if ($val) {
+						$item->setSourceKey($val);
+					}
 					break;
 				
 				case 'creators':