diff --git a/chrome/content/zotero/xpcom/data/item.js b/chrome/content/zotero/xpcom/data/item.js
index b303a2507c..f5a1fed28c 100644
--- a/chrome/content/zotero/xpcom/data/item.js
+++ b/chrome/content/zotero/xpcom/data/item.js
@@ -4423,7 +4423,9 @@ Zotero.Item.prototype.fromJSON = function (json, options = {}) {
 		}
 	}
 	
-	this.setField('extra', Zotero.Utilities.Internal.combineExtraFields(extra, extraFields));
+	if (extra || extraFields.size || this.getField('extra')) {
+		this.setField('extra', Zotero.Utilities.Internal.combineExtraFields(extra, extraFields));
+	}
 	
 	if (json.collections || this._collections.length) {
 		this.setCollections(json.collections);