Index: /trunk/doc/manual/en_US/user_VBoxManage.xml
===================================================================
--- /trunk/doc/manual/en_US/user_VBoxManage.xml	(revision 44128)
+++ /trunk/doc/manual/en_US/user_VBoxManage.xml	(revision 44129)
@@ -2230,5 +2230,8 @@
           zero the free disk space before compressing the virtual disk
           image. For Linux, use the <code>zerofree</code> utility which
-          supports ext2/ext3 filesystems.</para>
+          supports ext2/ext3 filesystems. For Mac OS X guests, use the
+          <emphasis>Erase Free Space</emphasis> feature of the built-in
+          <emphasis>Disk Utility</emphasis>. Use
+          <emphasis>Zero Out Data</emphasis> there.</para>
 
           <para>Please note that compacting is currently only available for