diff --git a/manpages/shorewall-tcclasses.xml b/manpages/shorewall-tcclasses.xml
index a6c1bc24c..b021e4ade 100644
--- a/manpages/shorewall-tcclasses.xml
+++ b/manpages/shorewall-tcclasses.xml
@@ -126,8 +126,10 @@
           url="http://www.shorewall.net/FAQ.htm#faq18">http://www.shorewall.net/FAQ.htm#faq18</ulink></para>
 
           <para>You may specify the interface number rather than the interface
-          name. If the <emphasis role="bold">classify</emphasis> option is
-          given for the interface in <ulink
+          name; if the class number is not numeric (e.g, contains a-f or A-f),
+          then it must be preceded by '0x' (e.g., 0xA). If the <emphasis
+          role="bold">classify</emphasis> option is given for the interface in
+          <ulink
           url="shorewall-tcdevices.html">shorewall-tcdevices</ulink>(5), then
           you must also specify an interface class (an integer that must be
           unique within classes associated with this interface). If the
diff --git a/manpages6/shorewall6-tcclasses.xml b/manpages6/shorewall6-tcclasses.xml
index c7ead115c..7e4f9a902 100644
--- a/manpages6/shorewall6-tcclasses.xml
+++ b/manpages6/shorewall6-tcclasses.xml
@@ -126,8 +126,10 @@
           url="http://www.shorewall.net/FAQ.htm#faq18">http://www.shorewall.net/FAQ.htm#faq18</ulink></para>
 
           <para>You may specify either the interface number or the interface
-          name. If the <emphasis role="bold">classify</emphasis> option is
-          given for the interface in <ulink
+          name; if the class number is not numeric (e.g, contains a-f or A-f),
+          then it must be preceded by '0x' (e.g., 0xA). If the <emphasis
+          role="bold">classify</emphasis> option is given for the interface in
+          <ulink
           url="shorewall6-tcdevices.html">shorewall6-tcdevices</ulink>(5),
           then you must also specify an interface class (an integer that must
           be unique within classes associated with this interface).</para>