diff --git a/middleman-cli/bin/middleman b/middleman-cli/bin/middleman
index ff61b21c..b5d1921d 100755
--- a/middleman-cli/bin/middleman
+++ b/middleman-cli/bin/middleman
@@ -22,12 +22,12 @@ module Middleman::Cli
       if setting.default.is_a?(String) || setting.default.is_a?(NilClass)
         base.class_option setting.key,
                           type: :string,
-                          default: setting.default,
+                          default: :undefined,
                           desc: setting.description
       elsif setting.default.is_a?(TrueClass) || setting.default.is_a?(FalseClass)
         base.class_option setting.key,
                           type: :boolean,
-                          default: setting.default,
+                          default: :undefined,
                           desc: setting.description
       end
     end
diff --git a/middleman-cli/lib/middleman-cli/build.rb b/middleman-cli/lib/middleman-cli/build.rb
index 4cddfe26..d6cf884b 100644
--- a/middleman-cli/lib/middleman-cli/build.rb
+++ b/middleman-cli/lib/middleman-cli/build.rb
@@ -63,14 +63,9 @@ module Middleman::Cli
         @app = ::Middleman::Application.new do
           config[:mode] = :build
           config[:show_exceptions] = false
-
-          cli_options.each do |k, v|
-            setting = config.setting(k.to_sym)
-            next unless setting
-
-            v = setting.options[:import].call(v) if setting.options[:import]
-
-            config[k.to_sym] = v
+          config[:cli_options] = cli_options.reduce({}) do |sum, (k, v)|
+            sum[k] = v unless v == :undefined
+            sum
           end
         end
 
diff --git a/middleman-core/lib/middleman-core/application.rb b/middleman-core/lib/middleman-core/application.rb
index 8951449d..16ddd59b 100644
--- a/middleman-core/lib/middleman-core/application.rb
+++ b/middleman-core/lib/middleman-core/application.rb
@@ -194,6 +194,8 @@ module Middleman
 
     define_setting :skip_build_clean, proc { |p| [/\.git/].any? { |r| p =~ r } }, 'Whether some paths should not be removed during a clean build.'
 
+    define_setting :cli_options, {}, 'Options from the Command Line.'
+
     define_setting :watcher_disable, false, 'If the Listen watcher should not run'
     define_setting :watcher_force_polling, false, 'If the Listen watcher should run in polling mode'
     define_setting :watcher_latency, nil, 'The Listen watcher latency'
@@ -281,6 +283,15 @@ module Middleman
       # Run any `configure` blocks for the current mode.
       execute_callbacks([:configure, config[:mode]])
 
+      config[:cli_options].each do |k, v|
+        setting = config.setting(k.to_sym)
+        next unless setting
+
+        v = setting.options[:import].call(v) if setting.options[:import]
+
+        config[k.to_sym] = v
+      end
+
       # Post parsing, pre-extension callback
       execute_callbacks(:after_configuration_eval)
 
diff --git a/middleman-core/lib/middleman-core/preview_server.rb b/middleman-core/lib/middleman-core/preview_server.rb
index 34b5d9c7..f2c571b5 100644
--- a/middleman-core/lib/middleman-core/preview_server.rb
+++ b/middleman-core/lib/middleman-core/preview_server.rb
@@ -140,13 +140,9 @@ module Middleman
         )
 
         app = ::Middleman::Application.new do
-          cli_options.each do |k, v|
-            setting = config.setting(k.to_sym)
-            next unless setting
-
-            v = setting.options[:import].call(v) if setting.options[:import]
-
-            config[k.to_sym] = v
+          cli_options.reduce({}) do |sum, (k, v)|
+            sum[k] = v unless v == :undefined
+            sum
           end
 
           ready do