diff --git a/app/controllers/user_avatars_controller.rb b/app/controllers/user_avatars_controller.rb
index b8f1a3492..80093b600 100644
--- a/app/controllers/user_avatars_controller.rb
+++ b/app/controllers/user_avatars_controller.rb
@@ -24,7 +24,7 @@ class UserAvatarsController < ApplicationController
     params.require(:version)
     params.require(:size)
 
-    return render_dot if params[:version].to_i > LetterAvatar::VERSION
+    return render_dot if params[:version] != LetterAvatar.version
 
     image = LetterAvatar.generate(params[:username].to_s, params[:size].to_i)
 
diff --git a/app/views/common/_discourse_javascript.html.erb b/app/views/common/_discourse_javascript.html.erb
index 8f0c83dd7..7beae7ecb 100644
--- a/app/views/common/_discourse_javascript.html.erb
+++ b/app/views/common/_discourse_javascript.html.erb
@@ -32,7 +32,7 @@
   Discourse.BaseUri = '<%= Discourse::base_uri "/" %>';
   Discourse.Environment = '<%= Rails.env %>';
   Discourse.SiteSettings = PreloadStore.get('siteSettings');
-  Discourse.LetterAvatarVersion = <%= LetterAvatar::VERSION %>;
+  Discourse.LetterAvatarVersion = '<%= LetterAvatar.version %>';
   PreloadStore.get("customEmoji").forEach(function(emoji) {
     Discourse.Dialect.registerEmoji(emoji.name, emoji.url);
   });
diff --git a/lib/letter_avatar.rb b/lib/letter_avatar.rb
index 48d333f4e..c05006882 100644
--- a/lib/letter_avatar.rb
+++ b/lib/letter_avatar.rb
@@ -23,8 +23,12 @@ class LetterAvatar
       end
     end
 
+    def version
+      "2_#{image_magick_version}"
+    end
+
     def cache_path
-      "public/uploads/letter_avatars/#{VERSION}"
+      "public/uploads/letter_avatars/#{version}"
     end
 
     def generate(username, size, opts = nil)
@@ -93,6 +97,27 @@ class LetterAvatar
       r,g,b = color
       "'rgb(#{r},#{g},#{b})'"
     end
+
+    def image_magick_version
+      @image_magick_version ||=
+        begin
+          Thread.new do
+            sleep 2
+            cleanup_old
+          end
+          Digest::MD5.hexdigest(`convert --version` << `convert -list font`)
+        end
+    end
+
+    def cleanup_old
+      skip = File.basename(cache_path)
+      parent_path = File.dirname(cache_path)
+      Dir.entries(parent_path).each do |path|
+        unless ['.','..'].include?(path) || path == skip
+          FileUtils.rm_rf(parent_path + "/" + path)
+        end
+      end
+    end
   end
 
   # palette of optimally disctinct colors
diff --git a/spec/components/letter_avatar_spec.rb b/spec/components/letter_avatar_spec.rb
new file mode 100644
index 000000000..9f5574b99
--- /dev/null
+++ b/spec/components/letter_avatar_spec.rb
@@ -0,0 +1,15 @@
+require 'spec_helper'
+require 'letter_avatar'
+
+describe LetterAvatar do
+  it "can cleanup correctly" do
+    path = LetterAvatar.cache_path
+
+    FileUtils.mkdir_p(path + "junk")
+    LetterAvatar.generate("test", 100)
+
+    LetterAvatar.cleanup_old
+
+    Dir.entries(File.dirname(path)).length.should == 3
+  end
+end