diff --git a/app/controllers/user_avatars_controller.rb b/app/controllers/user_avatars_controller.rb
index 1ecdb2be3..170767eaf 100644
--- a/app/controllers/user_avatars_controller.rb
+++ b/app/controllers/user_avatars_controller.rb
@@ -50,7 +50,7 @@ class UserAvatarsController < ApplicationController
 
   def show_in_site(hostname)
     size = params[:size].to_i
-    return render_dot unless Discourse.avatar_sizes.include?(size)
+
 
     username = params[:username].to_s
     return render_dot unless user = User.find_by(username_lower: username.downcase)
@@ -58,11 +58,21 @@ class UserAvatarsController < ApplicationController
     version = params[:version].to_i
     return render_dot unless version > 0 && user_avatar = user.user_avatar
 
+    # some sanity checks
+    if size < 8 || size > 500
+      return render_dot
+    end
+
+    if !Discourse.avatar_sizes.include?(size) && Discourse.store.external?
+      closest = Discourse.avatar_sizes.to_a.min{|a,b| (size-a).abs <=> (size-b).abs}
+      return redirect_to cdn_path("/user_avatar/#{params[:hostname]}/#{user.username_lower}/#{closest}/#{version}.png")
+    end
+
     upload = Upload.find_by(id: version) if user_avatar.contains_upload?(version)
     upload ||= user.uploaded_avatar if user.uploaded_avatar_id == version
 
     if user.uploaded_avatar && !upload
-      return redirect_to path("/user_avatar/#{hostname}/#{user.username_lower}/#{size}/#{user.uploaded_avatar_id}.png")
+      return redirect_to cdn_path("/user_avatar/#{hostname}/#{user.username_lower}/#{size}/#{user.uploaded_avatar_id}.png")
     elsif upload
       original = Discourse.store.path_for(upload)
       if Discourse.store.external? || File.exists?(original)
diff --git a/lib/discourse.rb b/lib/discourse.rb
index 8e838b1e0..46efbbc4f 100644
--- a/lib/discourse.rb
+++ b/lib/discourse.rb
@@ -79,7 +79,13 @@ module Discourse
   end
 
   def self.avatar_sizes
-    @avatar_size ||= Set.new(SiteSetting.avatar_sizes.split("|").map(&:to_i))
+    # Don't cache until we can get a notification from site settings to expire cache
+    set = Set.new(SiteSetting.avatar_sizes.split("|").map(&:to_i))
+    # add retinas which are 2x dpi
+    set.to_a.each do |size|
+      set << size*2
+    end
+    set
   end
 
   def self.activate_plugins!
diff --git a/lib/global_path.rb b/lib/global_path.rb
index 857679899..20f09f18b 100644
--- a/lib/global_path.rb
+++ b/lib/global_path.rb
@@ -2,4 +2,8 @@ module GlobalPath
   def path(p)
     "#{GlobalSetting.relative_url_root}#{p}"
   end
+
+  def cdn_path(p)
+    "#{GlobalSetting.cdn_url}#{path(p)}"
+  end
 end
diff --git a/spec/controllers/user_avatars_controller_spec.rb b/spec/controllers/user_avatars_controller_spec.rb
new file mode 100644
index 000000000..f25f0d3e4
--- /dev/null
+++ b/spec/controllers/user_avatars_controller_spec.rb
@@ -0,0 +1,35 @@
+require 'spec_helper'
+
+describe UserAvatarsController do
+
+  context 'show' do
+    it 'redirects to correct size for non local' do
+      SiteSetting.avatar_sizes = "100|49"
+      SiteSetting.enable_s3_uploads = true
+      SiteSetting.s3_access_key_id = "XXX"
+      SiteSetting.s3_secret_access_key = "XXX"
+      SiteSetting.s3_upload_bucket = "test"
+
+      GlobalSetting.expects(:cdn_url).returns("http://awesome.com/boom")
+
+
+      upload = Fabricate(:upload)
+      user = Fabricate(:user, uploaded_avatar_id: upload.id)
+
+      get :show, size: 97, username: user.username, version: upload.id, hostname: 'default'
+
+      # 98 is closese which is 49 * 2 for retina
+      expect(response).to redirect_to("http://awesome.com/boom/user_avatar/default/#{user.username_lower}/98/#{upload.id}.png")
+    end
+
+    it 'serves image even if size missing and its in local mode' do
+      SiteSetting.avatar_sizes = "50"
+
+      upload = Fabricate(:upload)
+      user = Fabricate(:user, uploaded_avatar_id: upload.id)
+
+      get :show, size: 51, username: user.username, version: upload.id, hostname: 'default'
+      expect(response).to be_success
+    end
+  end
+end
diff --git a/spec/models/upload_spec.rb b/spec/models/upload_spec.rb
index 092006b38..9cf928166 100644
--- a/spec/models/upload_spec.rb
+++ b/spec/models/upload_spec.rb
@@ -2,12 +2,6 @@ require 'spec_helper'
 require 'digest/sha1'
 
 describe Upload do
-  it { is_expected.to belong_to :user }
-
-  it { is_expected.to have_many :post_uploads }
-  it { is_expected.to have_many :posts }
-
-  it { is_expected.to have_many :optimized_images }
 
   let(:upload) { build(:upload) }
   let(:thumbnail) { build(:optimized_image, upload: upload) }