diff --git a/app/assets/javascripts/discourse/components/user-selector.js.es6 b/app/assets/javascripts/discourse/components/user-selector.js.es6
index 19c12841b5c..15d50faedae 100644
--- a/app/assets/javascripts/discourse/components/user-selector.js.es6
+++ b/app/assets/javascripts/discourse/components/user-selector.js.es6
@@ -25,6 +25,7 @@ export default TextField.extend({
       allowAny: this.get('allowAny'),
 
       dataSource: function(term) {
+        term = term.replace(/[^a-zA-Z0-9_]/, '');
         return userSearch({
           term: term,
           topicId: self.get('topicId'),
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index 6f80709df49..75ac418fb90 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -231,8 +231,8 @@ en:
             base:
               warning_requires_pm: "You can only attach warnings to private messages."
               too_many_users: "You can only send warnings to one user at a time."
-            archetype:
               cant_send_pm: "Sorry, you cannot send a private message to that user."
+              no_user_selected: "You must select a valid user."
         user:
           attributes:
             password:
diff --git a/lib/topic_creator.rb b/lib/topic_creator.rb
index 42b7d94e1a1..035af608872 100644
--- a/lib/topic_creator.rb
+++ b/lib/topic_creator.rb
@@ -114,7 +114,7 @@ class TopicCreator
     @topic.subtype = TopicSubtype.user_to_user unless @topic.subtype
 
     unless @opts[:target_usernames].present? || @opts[:target_group_names].present?
-      @topic.errors.add(:archetype, :cant_send_pm)
+      @topic.errors.add(:base, :no_user_selected)
       @errors = @topic.errors
       raise ActiveRecord::Rollback.new
     end
@@ -150,7 +150,7 @@ class TopicCreator
 
   def check_can_send_permission!(topic,item)
     unless @guardian.can_send_private_message?(item)
-      topic.errors.add(:archetype, :cant_send_pm)
+      topic.errors.add(:base, :cant_send_pm)
       @errors = topic.errors
       raise ActiveRecord::Rollback.new
     end