diff --git a/chrome/content/zotero/xpcom/http.js b/chrome/content/zotero/xpcom/http.js
index fa948cf93..c551a1ade 100644
--- a/chrome/content/zotero/xpcom/http.js
+++ b/chrome/content/zotero/xpcom/http.js
@@ -40,6 +40,7 @@ Zotero.HTTP = new function() {
 	 *         <li>cookieSandbox - The sandbox from which cookies should be taken</li>
 	 *         <li>debug - Log response text and status code</li>
 	 *         <li>dontCache - If set, specifies that the request should not be fulfilled from the cache</li>
+	 *         <li>headers - HTTP headers to include in the request</li>
 	 *         <li>responseType - The type of the response. See XHR 2 documentation for legal values</li>
 	 *         <li>responseCharset - The charset the response should be interpreted as</li>
 	 *         <li>successCodes - HTTP status codes that are considered successful</li>
diff --git a/chrome/content/zotero/xpcom/storage/zfs.js b/chrome/content/zotero/xpcom/storage/zfs.js
index e8b721191..1309b68c9 100644
--- a/chrome/content/zotero/xpcom/storage/zfs.js
+++ b/chrome/content/zotero/xpcom/storage/zfs.js
@@ -27,6 +27,9 @@
 Zotero.Sync.Storage.ZFS = (function () {
 	var _rootURI;
 	var _userURI;
+	var _headers = {
+		"Zotero-API-Version" : ZOTERO_CONFIG.API_VERSION
+	};
 	var _cachedCredentials = false;
 	
 	/**
@@ -38,7 +41,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 	function getStorageFileInfo(item) {
 		var funcName = "Zotero.Sync.Storage.ZFS.getStorageFileInfo()";
 		
-		return Zotero.HTTP.promise("GET", getItemInfoURI(item), { successCodes: [200, 404] })
+		return Zotero.HTTP.promise("GET", getItemInfoURI(item), { successCodes: [200, 404], headers: _headers })
 			.then(function (req) {
 				if (req.status == 404) {
 					return false;
@@ -232,7 +235,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 			body += "&zip=1";
 		}
 		
-		return Zotero.HTTP.promise("POST", uri, { body: body, debug: true })
+		return Zotero.HTTP.promise("POST", uri, { body: body, headers: _headers, debug: true })
 			.then(function (req) {
 				if (!req.responseXML) {
 					throw new Error("Invalid response retrieving file upload parameters");
@@ -508,7 +511,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 		var body = "update=" + uploadKey + "&mtime=" + item.attachmentModificationTime;
 		
 		// Register upload on server
-		return Zotero.HTTP.promise("POST", uri, { body: body, successCodes: [204] })
+		return Zotero.HTTP.promise("POST", uri, { body: body, headers: _headers, successCodes: [204] })
 			.then(function (req) {
 				updateItemFileInfo(item);
 				return {
@@ -886,7 +889,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 		})
 		.then(function () {
 			return Zotero.HTTP.promise("GET", lastSyncURI,
-				{ debug: true, successCodes: [200, 404] });
+				{ headers: _headers, successCodes: [200, 404], debug: true });
 		})
 		.then(function (req) {
 			// Not yet synced
@@ -929,7 +932,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 		
 		var lastSyncURI = this._getLastSyncURI(libraryID);
 		
-		return Zotero.HTTP.promise("POST", lastSyncURI, { debug: true, successCodes: [200, 404] })
+		return Zotero.HTTP.promise("POST", lastSyncURI, { headers: _headers, successCodes: [200, 404], debug: true })
 			.then(function (req) {
 				// Not yet synced
 				//
@@ -987,7 +990,7 @@ Zotero.Sync.Storage.ZFS = (function () {
 		// TODO: move to root uri
 		uri.spec += "?auth=1";
 		
-		return Zotero.HTTP.promise("GET", uri).
+		return Zotero.HTTP.promise("GET", uri, { headers: _headers }).
 			then(function (req) {
 				Zotero.debug("Credentials are cached");
 				_cachedCredentials = true;
diff --git a/chrome/content/zotero/xpcom/zotero.js b/chrome/content/zotero/xpcom/zotero.js
index 29120cb00..6f7f52c57 100644
--- a/chrome/content/zotero/xpcom/zotero.js
+++ b/chrome/content/zotero/xpcom/zotero.js
@@ -33,6 +33,7 @@ const ZOTERO_CONFIG = {
 	WWW_BASE_URL: 'http://www.zotero.org/',
 	SYNC_URL: 'https://sync.zotero.org/',
 	API_URL: 'https://api.zotero.org/',
+	API_VERSION: 2,
 	PREF_BRANCH: 'extensions.zotero.',
 	BOOKMARKLET_URL: 'https://www.zotero.org/bookmarklet/',
 	VERSION: "3.1a1.SOURCE"