diff --git a/middleman-core/lib/middleman-core/core_extensions/request.rb b/middleman-core/lib/middleman-core/core_extensions/request.rb
index dd6c7685..a8bc3a36 100644
--- a/middleman-core/lib/middleman-core/core_extensions/request.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/request.rb
@@ -251,7 +251,7 @@ module Middleman
           current_path = resource.destination_path
 
           # Set a HTTP content type based on the request's extensions
-          content_type(res, resource.mime_type)
+          content_type(res, mime_type(resource.ext))
 
           begin
             # Write out the contents of the page
@@ -280,6 +280,7 @@ module Middleman
         # @return [void]
         def mime_type(type, value=nil)
           return type if type.nil? || type.to_s.include?('/')
+          return ::Rack::Mime.mime_type('.txt') if type.empty?
           type = ".#{type}" unless type.to_s[0] == ?.
           return ::Rack::Mime.mime_type(type, nil) unless value
           ::Rack::Mime::MIME_TYPES[type] = value
@@ -314,7 +315,7 @@ module Middleman
         # @param [Hash] params
         # @return [void]
         def content_type(res, type, params={})
-          return res['Content-Type'] unless type
+          return unless type
           default = params.delete :default
           mime_type = mime_type(type) || default
           throw "Unknown media type: %p" % type if mime_type.nil?
diff --git a/middleman-core/lib/middleman-core/sitemap/resource.rb b/middleman-core/lib/middleman-core/sitemap/resource.rb
index 87bb610e..50179b8c 100644
--- a/middleman-core/lib/middleman-core/sitemap/resource.rb
+++ b/middleman-core/lib/middleman-core/sitemap/resource.rb
@@ -102,12 +102,6 @@ module Middleman
         File.extname(path)
       end
 
-      # Mime type of the path
-      # @return [String]
-      def mime_type
-        app.mime_type ext
-      end
-
       # Render this resource
       # @return [String]
       def render(opts={}, locs={}, &block)