diff --git a/lib/httpx/options.rb b/lib/httpx/options.rb
index b53e6b78..fae71577 100644
--- a/lib/httpx/options.rb
+++ b/lib/httpx/options.rb
@@ -30,6 +30,7 @@ module HTTPX
       :request_body_class => Class.new(Request::Body),
       :response_body_class => Class.new(Response::Body),
       :connection_class => Class.new(Connection),
+      :options_class => Class.new(self),
       :transport => nil,
       :transport_options => nil,
       :addresses => nil,
@@ -56,24 +57,20 @@ module HTTPX
 
         attr_reader(optname)
 
-        alias_method(:"__set_#{optname}", meth)
-
         class_eval(<<-OUT, __FILE__, __LINE__ + 1)
           def #{optname}=(value)
             return if value.nil?
 
-            value = __set_#{optname}(value)
+            value = #{meth}(value)
 
-            @#{optname} = value.freeze
+            @#{optname} = value
           end
           protected :#{optname}=
         OUT
-
-        remove_method(meth)
       end
 
       def def_option(optname, *args, &block)
-        if args.size.zero?
+        if args.size.zero? && !block_given?
           class_eval(<<-OUT, __FILE__, __LINE__ + 1)
             def option_#{optname}(v); v; end
           OUT
@@ -84,8 +81,8 @@ module HTTPX
       end
 
       def deprecated_def_option(optname, layout = nil, &interpreter)
-        warn "DEPRECATION WARNING: using `#{__method__}` for setting options is deprecated. " \
-          "Use `def option_\#{optname}` instead."
+        warn "DEPRECATION WARNING: using `def_option(#{optname})` for setting options is deprecated. " \
+          "Define module OptionsMethods and `def option_#{optname}(val)` instead."
 
         if layout
           class_eval(<<-OUT, __FILE__, __LINE__ + 1)
@@ -94,7 +91,7 @@ module HTTPX
             end
           OUT
         elsif block_given?
-          define_method(:"option:#{name}") do |value|
+          define_method(:"option_#{optname}") do |value|
             instance_exec(value, &interpreter)
           end
         end
@@ -171,7 +168,8 @@ module HTTPX
 
     %i[
       params form json body ssl http2_settings
-      request_class response_class headers_class request_body_class response_body_class connection_class
+      request_class response_class headers_class request_body_class
+      response_body_class connection_class options_class
       io fallback_protocol debug debug_level transport_options resolver_class resolver_options
       persistent
     ].each do |method_name|
diff --git a/lib/httpx/session.rb b/lib/httpx/session.rb
index 374a5560..924740ea 100644
--- a/lib/httpx/session.rb
+++ b/lib/httpx/session.rb
@@ -247,9 +247,8 @@ module HTTPX
         if !@plugins.include?(pl)
           @plugins << pl
           pl.load_dependencies(self, &block) if pl.respond_to?(:load_dependencies)
+
           @default_options = @default_options.dup
-          @default_options = pl.extra_options(@default_options, &block) if pl.respond_to?(:extra_options)
-          @default_options = @default_options.merge(options) if options
 
           include(pl::InstanceMethods) if defined?(pl::InstanceMethods)
           extend(pl::ClassMethods) if defined?(pl::ClassMethods)
@@ -266,14 +265,26 @@ module HTTPX
           opts.response_body_class.__send__(:include, pl::ResponseBodyMethods) if defined?(pl::ResponseBodyMethods)
           opts.response_body_class.extend(pl::ResponseBodyClassMethods) if defined?(pl::ResponseBodyClassMethods)
           opts.connection_class.__send__(:include, pl::ConnectionMethods) if defined?(pl::ConnectionMethods)
+          if defined?(pl::OptionsMethods)
+            opts.options_class.__send__(:include, pl::OptionsMethods)
+
+            (pl::OptionsMethods.instance_methods - Object.instance_methods).each do |meth|
+              opts.options_class.method_added(meth)
+            end
+            @default_options = opts.options_class.new(@default_options)
+          end
+
+          @default_options = pl.extra_options(@default_options) if pl.respond_to?(:extra_options)
+          @default_options = @default_options.merge(options) if options
+
           pl.configure(self, &block) if pl.respond_to?(:configure)
 
           @default_options.freeze
         elsif options
           # this can happen when two plugins are loaded, an one of them calls the other under the hood,
           # albeit changing some default.
-          @default_options = @default_options.dup
-          @default_options = @default_options.merge(options)
+          @default_options = pl.extra_options(@default_options) if pl.respond_to?(:extra_options)
+          @default_options = @default_options.merge(options) if options
 
           @default_options.freeze
         end
diff --git a/test/options_test.rb b/test/options_test.rb
index e05f569e..be116fdb 100644
--- a/test/options_test.rb
+++ b/test/options_test.rb
@@ -107,6 +107,7 @@ class OptionsTest < Minitest::Test
       :request_body_class => bar.request_body_class,
       :response_body_class => bar.response_body_class,
       :connection_class => bar.connection_class,
+      :options_class => bar.options_class,
       :transport => nil,
       :transport_options => nil,
       :addresses => nil,
diff --git a/test/session_test.rb b/test/session_test.rb
index 7ead3a79..ba053b66 100644
--- a/test/session_test.rb
+++ b/test/session_test.rb
@@ -169,6 +169,11 @@ class SessionTest < Minitest::Test
         self.class.foo
       end
     end
+    self::OptionsMethods = Module.new do
+      def option_foo(v)
+        v
+      end
+    end
 
     def self.load_dependencies(mod)
       mod.__send__(:include, Module.new do
@@ -179,9 +184,7 @@ class SessionTest < Minitest::Test
     end
 
     def self.extra_options(options)
-      Class.new(options.class) do
-        def_option(:foo)
-      end.new(options).merge(foo: "options-foo")
+      options.merge(foo: "options-foo")
     end
 
     def self.configure(mod)