diff --git a/lib/active_model/ordered_set.rb b/lib/active_model/ordered_set.rb
deleted file mode 100644
index dd76ed41..00000000
--- a/lib/active_model/ordered_set.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-module ActiveModel
-  class OrderedSet
-    def initialize(array)
-      @array = array
-      @hash = {}
-
-      array.each do |item|
-        @hash[item] = true
-      end
-    end
-
-    def merge!(other)
-      other.each do |item|
-        next if @hash.key?(item)
-
-        @hash[item] = true
-        @array.push item
-      end
-    end
-
-    def to_a
-      @array
-    end
-  end
-end
diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index 74374455..38c0b222 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -1,6 +1,5 @@
 require "active_support/core_ext/class/attribute"
 require "active_support/core_ext/module/anonymous"
-require "set"
 
 module ActiveModel
   # Active Model Serializer
diff --git a/lib/active_model_serializers.rb b/lib/active_model_serializers.rb
index b190e7d7..55709e0e 100644
--- a/lib/active_model_serializers.rb
+++ b/lib/active_model_serializers.rb
@@ -2,7 +2,6 @@ require "active_support"
 require "active_support/core_ext/string/inflections"
 require "active_support/notifications"
 require "active_model"
-require "active_model/ordered_set"
 require "active_model/array_serializer"
 require "active_model/serializer"
 require "active_model/serializer/associations"