diff --git a/en_US.ISO8859-1/books/porters-handbook/book.sgml b/en_US.ISO8859-1/books/porters-handbook/book.sgml
index b1848d2076..726ada8821 100644
--- a/en_US.ISO8859-1/books/porters-handbook/book.sgml
+++ b/en_US.ISO8859-1/books/porters-handbook/book.sgml
@@ -9398,6 +9398,22 @@ bacula:*:910:</programlisting>
 
       </sect1>
 
+      <sect1 id="dads-pthread">
+	<title>Threading libraries</title>
+
+	<para>The threading library must be linked to the binaries
+	  using a special linker flag <literal>-pthread</literal> on
+	  &os;.  If a port insists on linking
+	  <literal>-lpthread</literal> or <literal>-lc_r</literal>
+	  directly, patch it to use <makevar>PTHREAD_LIBS</makevar>
+	  variable provided by the ports framework.  This variable
+	  usually has the value of <literal>-pthread</literal>, but
+	  on certain architectures and &os; versions it can have
+	  different values, so do not just hardcode
+	  <literal>-pthread</literal> into patches and always use
+	  <makevar>PTHREAD_LIBS</makevar>.</para>
+      </sect1>
+
       <sect1 id="dads-freedback">
 	<title>Feedback</title>