diff --git a/server.rb b/server.rb
index eed401ae..d7f1121e 100644
--- a/server.rb
+++ b/server.rb
@@ -11,7 +11,9 @@
 require 'webrick'
 require 'json'
 
-port = ENV['PORT'].nil? ? 3000 : ENV['PORT'].to_i
+# default port to 3000 or overwrite with PORT variable by running
+# $ PORT=3001 ruby server.rb
+port = ENV['PORT'] ? ENV['PORT'].to_i : 3000
 
 puts "Server started: http://localhost:#{port}/"