diff --git a/doc/guides/gc-arena-howto.md b/doc/guides/gc-arena-howto.md
index 974466d3b..31bee93f1 100644
--- a/doc/guides/gc-arena-howto.md
+++ b/doc/guides/gc-arena-howto.md
@@ -3,6 +3,7 @@
 _This is an English translation of [Matz's blog post][matz blog post]
 written in Japanese._
 _Some parts are updated to reflect recent changes._
+
 [matz blog post]: <https://www.rubyist.net/~matz/20130731.html>
 
 When you are extending mruby using C language, you may encounter