diff --git a/po/at-expand.pl b/po/at-expand.pl
index d4427b52..bc1a744c 100644
--- a/po/at-expand.pl
+++ b/po/at-expand.pl
@@ -21,10 +21,13 @@ my @translator_help = (
  "#. on.  A table of these expansions can be found below.  Note that\n",
  "#. %-expressions that begin with \"%D\" and \"%I\" are two-character\n",
  "#. expansions; so for example, \"%Iu\" expands to the inode's user id\n",
- "#. ownership field (inode->i_uid).\n",
+ "#. ownership field (inode->i_uid).  Also the \"%B\" expansion is special:\n",
+ "#. it can expand to either the string \"indirect block\" (possibly preceded\n",
+ "#. by the word \"double\" or \"triple\"), or the string \"block #\" immediately\n",
+ "#. followed by an integer indicating a block sequence number.\n",
  "#.  \n",
  "#.	%b	<blk>			block number\n",
- "#.	%B	<blkcount>		integer\n",
+ "#.	%B	\"indirect block\" | \"block #\"<blkcount>	string | string+integer\n",
  "#.	%c	<blk2>			block number\n",
  "#.	%Di	<dirent> -> ino		inode number\n",
  "#.	%Dn	<dirent> -> name	string\n",