diff --git a/chrome/content/zotero/xpcom/data/item.js b/chrome/content/zotero/xpcom/data/item.js
index f9ef40539c..c44ec70a78 100644
--- a/chrome/content/zotero/xpcom/data/item.js
+++ b/chrome/content/zotero/xpcom/data/item.js
@@ -4006,6 +4006,7 @@ Zotero.Item.prototype.fromJSON = function (json) {
 			}
 			if (field == 'accessDate') {
 				this.setField(field, val);
+				setFields[field] = true;
 			}
 			else {
 				this[field] = val;
@@ -4072,16 +4073,21 @@ Zotero.Item.prototype.fromJSON = function (json) {
 					+ this.libraryKey);
 				continue;
 			}
-			isValidForType[field] = Zotero.ItemFields.isValidForType(
-				Zotero.ItemFields.getFieldIDFromTypeAndBase(itemTypeID, fieldID) || fieldID,
-				this.itemTypeID
-			);
+			// Convert to base-mapped field if necessary, so that setFields has the base-mapped field
+			// when it's checked for values from getUsedFields() below
+			let origFieldID = fieldID;
+			let origField = field;
+			fieldID = Zotero.ItemFields.getFieldIDFromTypeAndBase(itemTypeID, fieldID) || fieldID;
+			if (origFieldID != fieldID) {
+				field = Zotero.ItemFields.getName(fieldID);
+			}
+			isValidForType[field] = Zotero.ItemFields.isValidForType(fieldID, this.itemTypeID);
 			if (!isValidForType[field]) {
-				Zotero.logError("Discarding invalid field '" + field + "' for type " + itemTypeID
+				Zotero.logError("Discarding invalid field '" + origField + "' for type " + itemTypeID
 					+ " for item " + this.libraryKey);
 				continue;
 			}
-			this.setField(field, json[field]);
+			this.setField(field, json[origField]);
 			setFields[field] = true;
 		}
 	}
@@ -4089,8 +4095,7 @@ Zotero.Item.prototype.fromJSON = function (json) {
 	// Clear existing fields not specified
 	var previousFields = this.getUsedFields(true);
 	for (let field of previousFields) {
-		// Invalid fields will already have been cleared by the type change
-		if (!setFields[field] && isValidForType[field]) {
+		if (!setFields[field] && isValidForType[field] !== false) {
 			this.setField(field, false);
 		}
 	}
diff --git a/test/tests/itemTest.js b/test/tests/itemTest.js
index 03cfe1f7ce..580b9e672d 100644
--- a/test/tests/itemTest.js
+++ b/test/tests/itemTest.js
@@ -1194,8 +1194,25 @@ describe("Zotero.Item", function () {
 			});
 		})
 	})
-
+	
 	describe("#fromJSON()", function () {
+		it("should clear missing fields", function* () {
+			var item = new Zotero.Item('book');
+			item.setField('title', 'Test');
+			item.setField('date', '2016');
+			item.setField('accessDate', '2015-06-07T20:56:00Z');
+			yield item.saveTx();
+			var json = item.toJSON();
+			// Remove fields, which should cause them to be cleared in fromJSON()
+			delete json.date;
+			delete json.accessDate;
+			
+			item.fromJSON(json);
+			assert.strictEqual(item.getField('title'), 'Test');
+			assert.strictEqual(item.getField('date'), '');
+			assert.strictEqual(item.getField('accessDate'), '');
+		});
+		
 		it("should ignore unknown fields", function* () {
 			var json = {
 				itemType: "journalArticle",