diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index e6ba06301d..0872084cf5 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require "active_support/core_ext/string/strip"
 require "yaml"
 
 class ErrorsTest < ActiveModel::TestCase