diff --git a/ruby/lib/jam_ruby/jam_tracks_manager.rb b/ruby/lib/jam_ruby/jam_tracks_manager.rb
index ee7318118..de72513b8 100644
--- a/ruby/lib/jam_ruby/jam_tracks_manager.rb
+++ b/ruby/lib/jam_ruby/jam_tracks_manager.rb
@@ -25,6 +25,9 @@ module JamRuby
         Dir.mktmpdir do |tmp_dir|
           jam_file_opts=""
           jam_track.jam_track_tracks.each do |jam_track_track|
+
+            next if jam_track_track.track_type == "Master" # master mixes do not go into the JKZ
+
             # use the jam_track_track ID as the filename.ogg/.wav, because it's important metadata
             nm = jam_track_track.id + File.extname(jam_track_track.filename)
             track_filename = File.join(tmp_dir, nm)