diff --git a/ruby/lib/jam_ruby/models/music_session_user_history.rb b/ruby/lib/jam_ruby/models/music_session_user_history.rb
index f287604ae..f5ffebd98 100644
--- a/ruby/lib/jam_ruby/models/music_session_user_history.rb
+++ b/ruby/lib/jam_ruby/models/music_session_user_history.rb
@@ -87,7 +87,7 @@ module JamRuby
     end
 
     def count_concurrent(in_out_times)
-      in_out_times.sort!
+      in_out_times.sort! { |a,b| a[0] <=> b[0] }
 
       max_concurrent = 0
       concurrent = 0