diff --git a/chrome/content/zotero/xpcom/storage/storageLocal.js b/chrome/content/zotero/xpcom/storage/storageLocal.js
index d98a93488..d261b22e9 100644
--- a/chrome/content/zotero/xpcom/storage/storageLocal.js
+++ b/chrome/content/zotero/xpcom/storage/storageLocal.js
@@ -539,7 +539,8 @@ Zotero.Sync.Storage.Local = {
 	 * @param {Boolean} [updateItem=FALSE] - Mark attachment item as unsynced
 	 */
 	setSyncedModificationTime: Zotero.Promise.coroutine(function* (itemID, mtime, updateItem) {
-		if (mtime < 0) {
+		mtime = parseInt(mtime)
+		if (isNaN(mtime) || mtime < 0) {
 			Components.utils.reportError("Invalid file mod time " + mtime
 				+ " in Zotero.Storage.setSyncedModificationTime()");
 			mtime = 0;
diff --git a/chrome/content/zotero/xpcom/storage/webdav.js b/chrome/content/zotero/xpcom/storage/webdav.js
index c04bf9300..31fe47eed 100644
--- a/chrome/content/zotero/xpcom/storage/webdav.js
+++ b/chrome/content/zotero/xpcom/storage/webdav.js
@@ -1188,7 +1188,7 @@ Zotero.Sync.Storage.Mode.WebDAV.prototype = {
 			yield this._deleteStorageFiles([item.key + ".prop"]).catch(function (e) {
 				Zotero.logError(e);
 			});
-			throw new Error(Zotero.Sync.Storage.WebDAV.defaultError);
+			throw new Error(Zotero.Sync.Storage.Mode.WebDAV.defaultError);
 		}
 		
 		return { mtime, md5 };
diff --git a/test/tests/webdavTest.js b/test/tests/webdavTest.js
index 98d2bc6c0..b894a784c 100644
--- a/test/tests/webdavTest.js
+++ b/test/tests/webdavTest.js
@@ -461,21 +461,27 @@ describe("Zotero.Sync.Storage.Mode.WebDAV", function () {
 			item.synced = true;
 			yield item.saveTx();
 			
+			var syncedModTime = Date.now() - 10000;
+			var syncedHash = "3a2f092dd62178eb8bbfda42e07e64da";
+			
 			yield Zotero.DB.executeTransaction(function* () {
 				// Set an mtime in the past
-				yield Zotero.Sync.Storage.Local.setSyncedModificationTime(
-					item.id,
-					new Date(Date.now() - 10000)
-				);
+				yield Zotero.Sync.Storage.Local.setSyncedModificationTime(item.id, syncedModTime);
 				// And a different hash
-				yield Zotero.Sync.Storage.Local.setSyncedHash(
-					item.id, "3a2f092dd62178eb8bbfda42e07e64da"
-				);
+				yield Zotero.Sync.Storage.Local.setSyncedHash(item.id, syncedHash);
 			});
 			
 			var mtime = yield item.attachmentModificationTime;
 			var hash = yield item.attachmentHash;
 			
+			setResponse({
+				method: "GET",
+				url: `zotero/${item.key}.prop`,
+				text: '<properties version="1">'
+					+ `<mtime>${syncedModTime}</mtime>`
+					+ `<hash>${syncedHash}</hash>`
+					+ '</properties>'
+			});
 			setResponse({
 				method: "DELETE",
 				url: `zotero/${item.key}.prop`,
@@ -493,7 +499,7 @@ describe("Zotero.Sync.Storage.Mode.WebDAV", function () {
 			});
 			
 			var result = yield engine.start();
-			assertRequestCount(3);
+			assertRequestCount(4);
 			
 			assert.isTrue(result.localChanges);
 			assert.isTrue(result.remoteChanges);