diff --git a/doc/build.html b/doc/build.html
index 002483ee0..0a82ca7f7 100644
--- a/doc/build.html
+++ b/doc/build.html
@@ -224,6 +224,7 @@ open an issue or send me a pull request if you have information for me about
 other 21st-century compilers)
 <li/> The standard C library
 <li/> <tt>flex</tt>
+<li/> <tt>automake</tt>, <tt>autoconf</tt>, and <tt>libtool</tt>, if you build with autoconfig
 </ul>
 
 <a id="Optional_external_dependencies"/><h2>Optional external dependencies</h2>
diff --git a/doc/content-for-build.html b/doc/content-for-build.html
index 51a65ca36..564556124 100644
--- a/doc/content-for-build.html
+++ b/doc/content-for-build.html
@@ -114,6 +114,7 @@ open an issue or send me a pull request if you have information for me about
 other 21st-century compilers)
 <li/> The standard C library
 <li/> <tt>flex</tt>
+<li/> <tt>automake</tt>, <tt>autoconf</tt>, and <tt>libtool</tt>, if you build with autoconfig
 </ul>
 
 <h2>Optional external dependencies</h2>