diff --git a/lib/jwt/jwk/rsa.rb b/lib/jwt/jwk/rsa.rb
index 4691de75..6d7d7b06 100644
--- a/lib/jwt/jwk/rsa.rb
+++ b/lib/jwt/jwk/rsa.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'forwardable'
+
 module JWT
   module JWK
     class RSA