diff --git a/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml b/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
--- a/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
+++ b/en_US.ISO8859-1/books/porters-handbook/slow-porting/chapter.xml
@@ -363,7 +363,9 @@
 	<replaceable>*</replaceable> indicates the pathname of the
 	file that is patched, such as
 	<filename>patch-Imakefile</filename> or
-	<filename>patch-src-config.h</filename>.</para>
+	<filename>patch-src-config.h</filename>. Patches with file
+	names which do not start with <filename>patch-*</filename>
+	will not be applied automatically.</para>
 
       <para>After the file has been modified, &man.diff.1; is used to
 	record the differences between the original and the modified
@@ -471,7 +473,13 @@
 	&os; versions or when a particular option is enabled or
 	disabled.  Conditional patches are specified by placing the
 	full paths to the patch files in
-	<varname>EXTRA_PATCHES</varname>.</para>
+	<varname>EXTRA_PATCHES</varname>.
+	Conditional patch file names usually start with
+	<filename>extra-</filename> although this is not necessary.
+	However their file names <emphasis>must not</emphasis> start
+	with <filename>patch-</filename>.  If they do, they will be
+	first applied unconditionally by the framework which is not
+	what you want.</para>
 
       <example xml:id="slow-patch-extra-ex1">
 	<title>Applying a Patch for a Specific &os; Version</title>