diff --git a/lib/rack/request.rb b/lib/rack/request.rb
index 4c4cf61..120c2bf 100644
--- a/lib/rack/request.rb
+++ b/lib/rack/request.rb
@@ -40,7 +40,7 @@ module Rack
     # For more information on the use of media types in HTTP, see:
     # http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.7
     def media_type
-      content_type && content_type.split(/\s*[;,]\s*/, 2).first.downcase
+      content_type && content_type.to_s.split(/\s*[;,]\s*/, 2).first.downcase
     end
 
     # The media type parameters provided in CONTENT_TYPE as a Hash, or