diff --git a/lib/octocatalog-diff/catalog-diff/differ.rb b/lib/octocatalog-diff/catalog-diff/differ.rb
index e05fce50..07e19e89 100644
--- a/lib/octocatalog-diff/catalog-diff/differ.rb
+++ b/lib/octocatalog-diff/catalog-diff/differ.rb
@@ -12,6 +12,8 @@
 require_relative '../util/util'
 require_relative 'filter'
 
+HashDiff = Hashdiff unless defined? HashDiff
+
 module OctocatalogDiff
   module CatalogDiff
     # Calculate the difference between two Puppet catalogs.