diff --git a/app/models/user.rb b/app/models/user.rb
index 91355ee..61ad511 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -9,6 +9,7 @@ class User < ActiveRecord::Base
   validates_uniqueness_of :user_name, :if => lambda { |x| x.facebook_id.nil? }
   validates_format_of :user_name, :with => /[\w_-]+/, :if => lambda { |x| x.facebook_id.nil? }
   validates_presence_of :facebook_id, :if => lambda { |x| x.user_name.to_s.empty? }
+  validate :user_name_is_alphanumeric
   
   has_many :photos, :dependent => :destroy
   has_many :votes, :dependent => :destroy, :order => 'votes.photo_id ASC'
@@ -39,6 +40,12 @@ class User < ActiveRecord::Base
   
   protected
   
+  def user_name_is_alphanumeric
+    if self.facebook_id.to_i == 0 and self.user_name.to_s =~ /[^A-Za-z0-9]/
+      self.errors.add(:user_name, 'has illegal characters')
+    end
+  end
+  
   def saltify_password
     return true unless self.facebook_id.nil?
     if !self.password.to_s.empty?