diff --git a/lib/spellr/tokenizer.rb b/lib/spellr/tokenizer.rb
index 118e552..d8e0f3d 100644
--- a/lib/spellr/tokenizer.rb
+++ b/lib/spellr/tokenizer.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require 'stringio'
 require_relative 'token'
 require_relative 'column_location'
 require_relative 'line_location'