diff --git a/activesupport/lib/active_support/core_ext/time/calculations.rb b/activesupport/lib/active_support/core_ext/time/calculations.rb
index 00078de692f2231b9d0051bbf61b6338d457fcec..5ed750afcc668593dcc470b0ff72b6059ac3f901 100644
--- a/activesupport/lib/active_support/core_ext/time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/time/calculations.rb
@@ -1,3 +1,5 @@
+require 'active_support/duration'
+
 module ActiveSupport #:nodoc:
   module CoreExtensions #:nodoc:
     module Time #:nodoc: