diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index e3b940e2d5..78620e1508 100755
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -228,6 +228,7 @@ def sync_default_gems(gem)
     `git checkout ext/etc/depend`
   when "date"
     rm_rf(%w[ext/date test/date])
+    cp_r("#{upstream}/doc/date", "doc")
     cp_r("#{upstream}/ext/date", "ext")
     cp_r("#{upstream}/lib", "ext/date")
     cp_r("#{upstream}/test/date", "test")