diff --git a/en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml b/en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
index 2e6dc4b966..fb4066258b 100644
--- a/en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
+++ b/en_US.ISO8859-1/books/porters-handbook/makefiles/chapter.xml
@@ -3575,6 +3575,14 @@ OPT6_DESC=	Describe OPT6</programlisting>
 
 	<programlisting>OPTIONS_SINGLE=		SG1
 OPTIONS_SINGLE_SG1=	OPT3 OPT4</programlisting>
+ 
+	<warning>
+	  <para>There <emphasis>must</emphasis> be one of each
+	    <literal>OPTIONS_SINGLE</literal> group selected at all
+	    time for the options to be valid.  One option of each
+	    group <emphasis>must</emphasis> be added to
+	    <varname>OPTIONS_DEFAULT</varname>.</para>
+	</warning>
 
 	<para><varname>OPTIONS</varname> can be grouped as radio
 	  choices, where none or only one choice from each group