diff --git a/MANIFEST b/MANIFEST
index 61e677e500..dcbbe05c74 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -110,6 +110,7 @@ lib/cgi/session.rb
 lib/cgi-lib.rb
 lib/complex.rb
 lib/date.rb
+lib/date/format.rb
 lib/date2.rb
 lib/debug.rb
 lib/delegate.rb