diff --git a/chrome/content/zotero/elements/attachmentPreview.js b/chrome/content/zotero/elements/attachmentPreview.js
index e8e1bb3205..e98e90ceaa 100644
--- a/chrome/content/zotero/elements/attachmentPreview.js
+++ b/chrome/content/zotero/elements/attachmentPreview.js
@@ -581,7 +581,7 @@
 
 		async _renderMedia() {
 			this.setPreviewStatus("loading");
-			let mediaLoadPromise = new Zotero.Promise.defer();
+			let mediaLoadPromise = Zotero.Promise.defer();
 			let mediaID = `${this.previewType}-preview`;
 			let media = this._id(mediaID);
 			// Create media element when needed to avoid unnecessarily loading libs like libavcodec, libvpx, etc.
diff --git a/test/tests/attachmentsTest.js b/test/tests/attachmentsTest.js
index d2caaf3c84..b0c9a28d50 100644
--- a/test/tests/attachmentsTest.js
+++ b/test/tests/attachmentsTest.js
@@ -391,7 +391,7 @@ describe("Zotero.Attachments", function() {
 		});
 
 		afterEach(async function () {
-			var defer = new Zotero.Promise.defer();
+			var defer = Zotero.Promise.defer();
 			httpd.stop(() => defer.resolve());
 			await defer.promise;
 		});
diff --git a/test/tests/dataObjectTest.js b/test/tests/dataObjectTest.js
index 44894c0f32..c6f428169f 100644
--- a/test/tests/dataObjectTest.js
+++ b/test/tests/dataObjectTest.js
@@ -307,7 +307,7 @@ describe("Zotero.DataObject", function() {
 			var item = yield createDataObject('item');
 			item.setTags(['a']);
 			
-			var deferred = new Zotero.Promise.defer();
+			var deferred = Zotero.Promise.defer();
 			var origFunc = Zotero.Notifier.queue.bind(Zotero.Notifier);
 			sinon.stub(Zotero.Notifier, "queue").callsFake(function (event, type, ids, extraData) {
 				// Add a new tag after the first one has been added to the DB and before the save is
diff --git a/test/tests/fileTest.js b/test/tests/fileTest.js
index 7dc0d529e0..9b9c192969 100644
--- a/test/tests/fileTest.js
+++ b/test/tests/fileTest.js
@@ -489,7 +489,7 @@ describe("Zotero.File", function () {
 		});
 
 		after(function* () {
-			var defer = new Zotero.Promise.defer();
+			var defer = Zotero.Promise.defer();
 			httpd.stop(() => defer.resolve());
 			yield defer.promise;
 		});
diff --git a/test/tests/httpTest.js b/test/tests/httpTest.js
index aa55b41c17..eeaefd6531 100644
--- a/test/tests/httpTest.js
+++ b/test/tests/httpTest.js
@@ -74,7 +74,7 @@ describe("Zotero.HTTP", function () {
 	});
 	
 	after(function* () {
-		var defer = new Zotero.Promise.defer();
+		var defer = Zotero.Promise.defer();
 		httpd.stop(() => defer.resolve());
 		yield defer.promise;
 		
diff --git a/test/tests/itemTreeTest.js b/test/tests/itemTreeTest.js
index f8973780c7..9080947124 100644
--- a/test/tests/itemTreeTest.js
+++ b/test/tests/itemTreeTest.js
@@ -1150,7 +1150,7 @@ describe("Zotero.ItemTree", function() {
 		});
 		
 		after(function* () {
-			var defer = new Zotero.Promise.defer();
+			var defer = Zotero.Promise.defer();
 			httpd.stop(() => defer.resolve());
 			yield defer.promise;
 			
diff --git a/test/tests/server_connectorIntegrationTest.js b/test/tests/server_connectorIntegrationTest.js
index 5e59c0e303..9eeaf0ec07 100644
--- a/test/tests/server_connectorIntegrationTest.js
+++ b/test/tests/server_connectorIntegrationTest.js
@@ -52,7 +52,7 @@ describe("Connector HTTP Integration Server", function () {
 	describe('/connector/document/respond', function () {
 		it('should pass along the request body via HTTPIntegrationClient', async function () {
 			try {
-				Zotero.HTTPIntegrationClient.deferredResponse = new Zotero.Promise.defer();
+				Zotero.HTTPIntegrationClient.deferredResponse = Zotero.Promise.defer();
 
 				let postBody = { outputFormat: 'html' };
 				Zotero.HTTP.request(
diff --git a/test/tests/server_connectorTest.js b/test/tests/server_connectorTest.js
index 8e91c81bd7..5cd43f3f22 100644
--- a/test/tests/server_connectorTest.js
+++ b/test/tests/server_connectorTest.js
@@ -47,7 +47,7 @@ describe("Connector Server", function () {
 	});
 	
 	afterEach(function* () {
-		var defer = new Zotero.Promise.defer();
+		var defer = Zotero.Promise.defer();
 		httpd.stop(() => defer.resolve());
 		yield defer.promise;
 	});
diff --git a/test/tests/zfsTest.js b/test/tests/zfsTest.js
index d69fa961a2..650b7e1731 100644
--- a/test/tests/zfsTest.js
+++ b/test/tests/zfsTest.js
@@ -99,7 +99,7 @@ describe("Zotero.Sync.Storage.Mode.ZFS", function () {
 	})
 	
 	afterEach(function* () {
-		var defer = new Zotero.Promise.defer();
+		var defer = Zotero.Promise.defer();
 		httpd.stop(() => defer.resolve());
 		yield defer.promise;
 		win.close();
diff --git a/test/tests/zoteroPaneTest.js b/test/tests/zoteroPaneTest.js
index a02ba11a20..556de052bc 100644
--- a/test/tests/zoteroPaneTest.js
+++ b/test/tests/zoteroPaneTest.js
@@ -236,7 +236,7 @@ describe("ZoteroPane", function() {
 			await Zotero.Users.setCurrentUsername("testuser");
 		})
 		afterEach(function* () {
-			var defer = new Zotero.Promise.defer();
+			var defer = Zotero.Promise.defer();
 			httpd.stop(() => defer.resolve());
 			yield defer.promise;
 		})