diff --git a/lib/rein.rb b/lib/rein.rb
index 29c748e..6bcde16 100644
--- a/lib/rein.rb
+++ b/lib/rein.rb
@@ -7,6 +7,7 @@ module Constraint
 
 require "active_record"
 require "active_support/core_ext/hash"
+require "active_support/inflector"
 
 require "rein/constraint/primary_key"
 require "rein/constraint/foreign_key"