diff --git a/app/assets/javascripts/discourse/templates/modal/create_account.js.handlebars b/app/assets/javascripts/discourse/templates/modal/create_account.js.handlebars
index 71735338033..aec6b0392cd 100644
--- a/app/assets/javascripts/discourse/templates/modal/create_account.js.handlebars
+++ b/app/assets/javascripts/discourse/templates/modal/create_account.js.handlebars
@@ -30,7 +30,7 @@
       <tr>
             <td><label for='new-account-username'>{{i18n user.username.title}}</label></td>
             <td>
-            {{view Ember.TextField valueBinding="view.accountUsername" id="new-account-username"}}
+            {{view Ember.TextField valueBinding="view.accountUsername" id="new-account-username" maxlength="15"}}
             &nbsp;{{view Discourse.InputTipView validationBinding="view.usernameValidation"}}
             </td>
       </tr>
diff --git a/app/assets/javascripts/discourse/templates/user/username.js.handlebars b/app/assets/javascripts/discourse/templates/user/username.js.handlebars
index affaa199861..97c5b934b7e 100644
--- a/app/assets/javascripts/discourse/templates/user/username.js.handlebars
+++ b/app/assets/javascripts/discourse/templates/user/username.js.handlebars
@@ -17,7 +17,7 @@
   <div class="control-group">
     <label class="control-label">{{i18n user.username.title}}</label>
     <div class="controls">
-      {{view Ember.TextField valueBinding="controller.newUsername" elementId="change_username" classNames="input-xxlarge"}}
+      {{view Ember.TextField valueBinding="controller.newUsername" elementId="change_username" classNames="input-xxlarge" maxlength="15"}}
     </div>
     <div class='instructions'>
       {{#if controller.taken}}
diff --git a/app/assets/javascripts/discourse/views/modal/create_account_view.js.coffee b/app/assets/javascripts/discourse/views/modal/create_account_view.js.coffee
index 8ee6d82d5c1..6ea7fd50768 100644
--- a/app/assets/javascripts/discourse/views/modal/create_account_view.js.coffee
+++ b/app/assets/javascripts/discourse/views/modal/create_account_view.js.coffee
@@ -69,6 +69,9 @@ window.Discourse.CreateAccountView = window.Discourse.ModalBodyView.extend Disco
     # If too short
     return Discourse.InputValidation.create(failed: true, reason: Em.String.i18n('user.username.too_short')) if @get('accountUsername').length < 3
 
+    # If too long
+    return Discourse.InputValidation.create(failed: true, reason: Em.String.i18n('user.username.too_long')) if @get('accountUsername').length > 15
+
     @checkUsernameAvailability()
 
     # Let's check it out asynchronously
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 57faf80c080..0500ade667a 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -504,6 +504,7 @@ en:
         global_mismatch: "Already registered. Try {{suggestion}}?"
         not_available: "Not available. Try {{suggestion}}?"
         too_short: "Your username is too short."
+        too_long: "Your username is too long."
         checking: "Checking username availability..."
         enter_email: 'Username found. Enter matching email.'