diff --git a/doc/ca65.sgml b/doc/ca65.sgml
index 1a82788f0..d8557bfdb 100644
--- a/doc/ca65.sgml
+++ b/doc/ca65.sgml
@@ -112,6 +112,7 @@ Long options:
   --include-dir dir	Set an include directory search path
   --listing		Create a listing if assembly was ok
   --list-bytes n	Maximum number of bytes per listing line
+  --macpack-dir dir	Set a macro package directory
   --memory-model model	Set the memory model
   --pagelength n	Set the page length for the listing
   --smart		Enable smart mode
@@ -190,6 +191,16 @@ Here is a description of all the command line options:
   number of printed bytes.
 
 
+  <tag><tt>--macpack-dir dir</tt></tag>
+
+  This options allows to specify a directory containing macro files that are
+  used instead of the builtin images when a <tt><ref id=".MACPACK"
+  name=".MACPACK"></tt> directive is encountered. If <tt>--macpack-dir</tt>
+  was specified, a <tt>.mac</tt> extension is added to the package name and
+  the resulting file is loaded from the given directory. This is most useful
+  when debugging the builtin macro packages.
+
+
   <tag><tt>-mm model, --memory-model model</tt></tag>
 
   Define the default memory model. Possible model specifiers are near, far and