diff --git a/lib/active_model/one_time_password.rb b/lib/active_model/one_time_password.rb
index c926abc..39eb8bd 100644
--- a/lib/active_model/one_time_password.rb
+++ b/lib/active_model/one_time_password.rb
@@ -114,7 +114,7 @@ def otp_counter=(attr)
       end
 
       def serializable_hash(options = nil)
-        options ||= {}
+        options = options ? options.dup : {}
         options[:except] = Array(options[:except])
         options[:except] << self.class.otp_column_name