diff --git a/lib/paperclip.rb b/lib/paperclip.rb
index 7989ac4..ccad9a7 100644
--- a/lib/paperclip.rb
+++ b/lib/paperclip.rb
@@ -42,12 +42,21 @@ require 'paperclip/matchers'
 require 'paperclip/callback_compatability'
 require 'paperclip/railtie' if defined?(Rails)
 
+require 'active_support/concern'
+require 'active_support/core_ext/class/attribute'
+
 # The base module that gets included in ActiveRecord::Base. See the
 # documentation for Paperclip::ClassMethods for more useful information.
 module Paperclip
-
   VERSION = "2.2.9.2"
 
+  extend ActiveSupport::Concern
+
+  included do
+    class_attribute :attachment_definitions
+    Paperclip::CallbackCompatability.install_to(self)
+  end
+
   class << self
     # Provides configurability to Paperclip. There are a number of options available, such as:
     # * whiny: Will raise an error if Paperclip cannot process thumbnails of
@@ -109,17 +118,6 @@ module Paperclip
       File.exist?("/dev/null") ? "/dev/null" : "NUL"
     end
 
-    def included base #:nodoc:
-      base.extend ClassMethods
-      base.class_attribute :attachment_definitions
-
-      if base.respond_to?(:set_callback)
-        base.send :include, Paperclip::CallbackCompatability::Rails3
-      else
-        base.send :include, Paperclip::CallbackCompatability::Rails21
-      end
-    end
-
     def processor name #:nodoc:
       name = name.to_s.camelize
       processor = Paperclip.const_get(name)
@@ -217,11 +215,7 @@ module Paperclip
     def has_attached_file name, options = {}
       include InstanceMethods
 
-      if attachment_definitions.nil?
-        self.attachment_definitions = {}
-      else
-        self.attachment_definitions = self.attachment_definitions.dup
-      end
+      self.attachment_definitions = self.attachment_definitions&.dup || {}
       attachment_definitions[name] = {:validations => []}.merge(options)
 
       after_save :save_attached_files
@@ -305,10 +299,6 @@ module Paperclip
                                                                      :if           => options[:if],
                                                                      :unless       => options[:unless]}]
     end
-
-    def attachment_definitions
-      self.attachment_definitions
-    end
   end
 
   module InstanceMethods #:nodoc:
diff --git a/lib/paperclip/callback_compatability.rb b/lib/paperclip/callback_compatability.rb
index eb9fe58..5de4201 100644
--- a/lib/paperclip/callback_compatability.rb
+++ b/lib/paperclip/callback_compatability.rb
@@ -1,11 +1,14 @@
 module Paperclip
   module CallbackCompatability
-    module Rails21
-      def self.included(base)
-        base.extend(Defining)
-        base.send(:include, Running)
-      end
+    module_function
 
+    def install_to(base)
+      mod = base.respond_to?(:set_callback) ? Rails3 : Rails21
+      base.extend(mod::Defining)
+      base.send(:include, mod::Running)
+    end
+
+    module Rails21
       module Defining
         def define_paperclip_callbacks(*args)
           args.each do |callback|
@@ -28,11 +31,6 @@ module Paperclip
     end
 
     module Rails3
-      def self.included(base)
-        base.extend(Defining)
-        base.send(:include, Running)
-      end
-
       module Defining
         def define_paperclip_callbacks(*callbacks)
           terminator =
@@ -43,14 +41,15 @@ module Paperclip
             end
           define_callbacks *[callbacks, {terminator: terminator}].flatten
           callbacks.each do |callback|
-            eval <<-end_callbacks
+            class_eval <<~RUBY, __FILE__, __LINE__ + 1
               def before_#{callback}(*args, &blk)
                 set_callback(:#{callback}, :before, *args, &blk)
               end
+
               def after_#{callback}(*args, &blk)
                 set_callback(:#{callback}, :after, *args, &blk)
               end
-            end_callbacks
+            RUBY
           end
         end
       end
@@ -60,9 +59,7 @@ module Paperclip
           run_callbacks(callback, &block)
         end
       end
-
     end
-
   end
 end
 
diff --git a/paperclip.gemspec b/paperclip.gemspec
index be76b92..4818a22 100644
--- a/paperclip.gemspec
+++ b/paperclip.gemspec
@@ -17,5 +17,6 @@ Gem::Specification.new do |s|
   s.rubygems_version = %q{1.3.1}
   s.summary = %q{File attachments as attributes for ActiveRecord}
 
+  s.add_dependency 'activesupport'
   s.add_dependency 'fastimage'
 end