diff --git a/lib/middleman/guard.rb b/lib/middleman/guard.rb
index 1437e60e..5e2e9216 100644
--- a/lib/middleman/guard.rb
+++ b/lib/middleman/guard.rb
@@ -62,7 +62,7 @@ module Guard
       }
       @server_job = fork do
         app = ::Middleman.server
-        app.set :environment, @options[:environment]
+        app.set :environment, @options[:environment].to_sym
         @server_options[:app] = app.new
         @server_options[:server] = 'thin'
         ::Rack::Server.new(@server_options).start