diff --git a/public/src/client/register.js b/public/src/client/register.js
index d2fca2b7f5..0a98b324fa 100644
--- a/public/src/client/register.js
+++ b/public/src/client/register.js
@@ -2,8 +2,8 @@
 
 
 define('forum/register', [
-	'translator', 'zxcvbn', 'slugify', 'jquery-form',
-], function (translator, zxcvbn, slugify) {
+	'translator', 'zxcvbn', 'slugify', 'api', 'jquery-form',
+], function (translator, zxcvbn, slugify, api) {
 	var Register = {};
 	var validationError = false;
 	var successIcon = '';
@@ -159,21 +159,14 @@ define('forum/register', [
 		} else if (!utils.isUserNameValid(username) || !slugify(username)) {
 			showError(username_notify, '[[error:invalid-username]]');
 		} else {
-			socket.emit('user.exists', {
-				username: username,
-			}, function (err, exists) {
-				if (err) {
-					return app.alertError(err.message);
-				}
-
-				if (exists) {
+			api.head(`/users/bySlug/${username}`, {})
+				.then(() => {
 					showError(username_notify, '[[error:username-taken]]');
-				} else {
+				})
+				.catch(() => {
 					showSuccess(username_notify, successIcon);
-				}
-
-				callback();
-			});
+				})
+				.finally(callback);
 		}
 	}
 
diff --git a/public/src/modules/api.js b/public/src/modules/api.js
index 7b01f367c1..207342d1c1 100644
--- a/public/src/modules/api.js
+++ b/public/src/modules/api.js
@@ -13,14 +13,17 @@ define('api', () => {
 			$.ajax(options)
 				.done((res) => {
 					cb(null,
-						res.hasOwnProperty('status') && res.hasOwnProperty('response') ?
-							res.response : res
+						res && res.hasOwnProperty('status') && res.hasOwnProperty('response') ?
+							res.response : (res || {})
 					);
 				})
 				.fail((ev) => {
-					const errMessage = ev.responseJSON.status && ev.responseJSON.status.message ?
-						ev.responseJSON.status.message :
-						ev.responseJSON.error;
+					let errMessage;
+					if (ev.responseJSON) {
+						errMessage = ev.responseJSON.status && ev.responseJSON.status.message ?
+							ev.responseJSON.status.message :
+							ev.responseJSON.error;
+					}
 
 					cb(new Error(errMessage || ev.statusText));
 				});
@@ -39,10 +42,15 @@ define('api', () => {
 		});
 	}
 
-	api.get = (route, payload, onSuccess) => call({
+	api.get = (route, payload = {}, onSuccess) => call({
 		url: route + (Object.keys(payload).length ? ('?' + $.param(payload)) : ''),
 	}, onSuccess);
 
+	api.head = (route, payload, onSuccess) => call({
+		url: route + (Object.keys(payload).length ? ('?' + $.param(payload)) : ''),
+		method: 'head',
+	}, onSuccess);
+
 	api.post = (route, payload, onSuccess) => call({
 		url: route,
 		method: 'post',
diff --git a/src/controllers/helpers.js b/src/controllers/helpers.js
index e64ac024b2..cf07d469cb 100644
--- a/src/controllers/helpers.js
+++ b/src/controllers/helpers.js
@@ -341,6 +341,10 @@ helpers.getHomePageRoutes = async function (uid) {
 };
 
 helpers.formatApiResponse = async (statusCode, res, payload) => {
+	if (res.req.method === 'HEAD') {
+		return res.sendStatus(statusCode);
+	}
+
 	if (String(statusCode).startsWith('2')) {
 		res.status(statusCode).json({
 			status: {
diff --git a/src/socket.io/user.js b/src/socket.io/user.js
index 4e5f9b06d1..292fb1ea48 100644
--- a/src/socket.io/user.js
+++ b/src/socket.io/user.js
@@ -30,6 +30,8 @@ require('./user/ban')(SocketUser);
 require('./user/registration')(SocketUser);
 
 SocketUser.exists = async function (socket, data) {
+	sockets.warnDeprecated(socket, 'HEAD /api/v3/users/bySlug/:userslug');
+
 	if (!data || !data.username) {
 		throw new Error('[[error:invalid-data]]');
 	}