diff --git a/lib/active_model_serializers/model.rb b/lib/active_model_serializers/model.rb
index ea10ac88..2ff3d60c 100644
--- a/lib/active_model_serializers/model.rb
+++ b/lib/active_model_serializers/model.rb
@@ -1,6 +1,7 @@
 # ActiveModelSerializers::Model is a convenient superclass for making your models
 # from Plain-Old Ruby Objects (PORO). It also serves as a reference implementation
 # that satisfies ActiveModel::Serializer::Lint::Tests.
+require 'active_support/core_ext/hash'
 module ActiveModelSerializers
   class Model
     include ActiveModel::Serializers::JSON