diff --git a/tool/lib/core_assertions.rb b/tool/lib/core_assertions.rb
index 47d711f4fa..d84b7f555a 100644
--- a/tool/lib/core_assertions.rb
+++ b/tool/lib/core_assertions.rb
@@ -33,6 +33,7 @@ module Test
     module CoreAssertions
       require_relative 'envutil'
       require 'pp'
+      require 'io/console'
 
       def mu_pp(obj) #:nodoc:
         obj.pretty_inspect.chomp