diff --git a/lib/has_friendship.rb b/lib/has_friendship.rb
index a6bcf30..0b6c8ca 100644
--- a/lib/has_friendship.rb
+++ b/lib/has_friendship.rb
@@ -1,3 +1,5 @@
+require 'stateful_enum'
+
 require 'active_support'
 require 'active_record'