diff --git a/middleman-core/lib/middleman-core/extensions/asset_host.rb b/middleman-core/lib/middleman-core/extensions/asset_host.rb
index 28765c24..07aac381 100644
--- a/middleman-core/lib/middleman-core/extensions/asset_host.rb
+++ b/middleman-core/lib/middleman-core/extensions/asset_host.rb
@@ -1,7 +1,7 @@
 require 'middleman-core/middleware/inline_url_rewriter'
 
 class Middleman::Extensions::AssetHost < ::Middleman::Extension
-  option :host, nil, 'The asset host to use or a Proc to determine asset host'
+  option :host, nil, 'The asset host to use or a Proc to determine asset host', required: true
   option :exts, %w(.css .png .jpg .jpeg .svg .svgz .js .gif), 'List of extensions that get cache busters strings appended to them.'
   option :sources, %w(.htm .html .php .css .js), 'List of extensions that are searched for bustable assets.'
   option :ignore, [], 'Regexes of filenames to skip adding query strings to'