diff --git a/doc/extension.ja.rdoc b/doc/extension.ja.rdoc
index 94581a9356..48699ac620 100644
--- a/doc/extension.ja.rdoc
+++ b/doc/extension.ja.rdoc
@@ -1865,7 +1865,8 @@ Ractor をサポートするための詳細は、{Appendix F. Ractor
 support}[rdoc-ref:extension.rdoc@Appendix+F.+Ractor+support]
 を参照してください。
 
-:stopdoc: Local variables:
-:stopdoc: fill-column: 60
-:stopdoc: end:
-:startdoc:
+--
+Local variables:
+fill-column: 60
+end:
+++
diff --git a/doc/extension.rdoc b/doc/extension.rdoc
index 703245be9c..01ac140e69 100644
--- a/doc/extension.rdoc
+++ b/doc/extension.rdoc
@@ -2274,7 +2274,8 @@ To make a "Ractor-safe" C extension, we need to check the following points:
    making of a Ractor-safe extension.  This document will be extended as they are
    discovered.
 
-:stopdoc: Local variables:
-:stopdoc: fill-column: 70
-:stopdoc: end:
-:startdoc:
+--
+Local variables:
+fill-column: 70
+end:
+++