diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index 6b90d91ed3..f646c6ff82 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -8,6 +8,7 @@
 end
 
 require "active_support/core_ext/enumerable"
+require "active_support/core_ext/marshal"
 require "active_support/core_ext/array/extract_options"
 
 module ActiveSupport