diff --git a/actionpack/lib/action_dispatch/http/mime_types.rb b/actionpack/lib/action_dispatch/http/mime_types.rb
index 9f8db397fd7fa3648227eadf69a2e9320e14a99f..cc41bdda5a1371e61ffdc888f863ee40f27139c6 100644
--- a/actionpack/lib/action_dispatch/http/mime_types.rb
+++ b/actionpack/lib/action_dispatch/http/mime_types.rb
@@ -24,7 +24,7 @@
 Mime::Type.register "audio/webm", :weba, [], %w(weba)
 Mime::Type.register "audio/ogg", :ogg, [], %w(oga ogg spx opus)
 Mime::Type.register "audio/aac", :acc, [], %w(aac)
-Mime::Type.register "audio/mp4", :mp4, [], %w(m4a mpg4)
+Mime::Type.register "audio/mp4", :m4a, [], %w(m4a mpg4)
 Mime::Type.register "audio/flac", :flac, [], %w(flac)
 
 Mime::Type.register "video/webm", :webm, [], %w(webm)