diff --git a/lib/hot_constants/hot_constants.rb b/lib/hot_constants/hot_constants.rb
index 84ee5ec..a60c1e7 100644
--- a/lib/hot_constants/hot_constants.rb
+++ b/lib/hot_constants/hot_constants.rb
@@ -3,11 +3,11 @@ require 'dotenv'
 # Hot Live Constants
 module HotConstants
   HOTENV = {} # rubocop:disable Style/MutableConstant
+  LISTENERS = {} # rubocop:disable Style/MutableConstant
   LOGGER = SemanticLogger[to_s]
 
   class << self
     def initialize
-      @on_change_listeners = {}
       env_sample = Dotenv.parse('.env.sample') # TODO: able to detect add/remove, then either call define_method or undef_method!
       env_sample.each do |key, value|
         dkey = key.downcase
@@ -20,15 +20,15 @@ module HotConstants
 
     def reload!
       HOTENV.replace Dotenv.parse # TODO: detect true changes before processing block below (or yield)
-      @on_change_listeners.each_pair do |key, block|
+      LISTENERS.each_pair do |key, block|
         old_value = nil # TODO: remember last previous value
         new_value = method(key).call
-        block.call(new_value)
+        block.call(new_value, old_value)
       end
     end
 
     def on_change(key, &block)
-      @on_change_listeners[key.downcase.to_sym] = block
+      LISTENERS[key.downcase.to_sym] = block
     end
 
     private