diff --git a/lib/middleman/base.rb b/lib/middleman/base.rb
index 9f7dc422..89f74a7e 100644
--- a/lib/middleman/base.rb
+++ b/lib/middleman/base.rb
@@ -36,7 +36,7 @@ module Middleman
     # Rack helper for adding mime-types during local preview
     def self.mime(ext, type)
       ext = ".#{ext}" unless ext.to_s[0] == ?.
-      Rack::Mime::MIME_TYPES[ext.to_s] = type
+      ::Rack::Mime::MIME_TYPES[ext.to_s] = type
     end
 
     # Convenience function to discover if a tempalte exists for the requested renderer (haml, sass, etc)
diff --git a/lib/middleman/rack/static.rb b/lib/middleman/rack/static.rb
index 6357b899..69d967a4 100644
--- a/lib/middleman/rack/static.rb
+++ b/lib/middleman/rack/static.rb
@@ -9,7 +9,8 @@ module Middleman
 
       def call(env)
         path = env["PATH_INFO"]
-        if path.include?("favicon.ico") || File.exists?(File.join(Middleman::Base.public, path))
+        file_path = File.join(Middleman::Base.public, path)
+        if path.include?("favicon.ico") || (File.exists?(file_path) && !File.directory?(file_path))
           @file_server.call(env)
         else
           @app.call(env)