diff --git a/texinfo.tex b/texinfo.tex
index 09f89687..d8eff35b 100644
--- a/texinfo.tex
+++ b/texinfo.tex
@@ -3636,8 +3636,8 @@ width0pt\relax} \fi
 % \nonarrowing is a flag.  If "set", @lisp etc don't narrow margins.
 \let\nonarrowing=\relax
 
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-% \cartouche: draw rectangle w/rounded corners around argument
+% @cartouche ... @end cartouche: draw rectangle w/rounded corners around
+% environment contents.
 \font\circle=lcircle10
 \newdimen\circthick
 \newdimen\cartouter\newdimen\cartinner
@@ -3664,9 +3664,9 @@ width0pt\relax} \fi
         \cartinner=\hsize \advance\cartinner by-\lskip
                           \advance\cartinner by-\rskip
         \cartouter=\hsize
-        \advance\cartouter by 18pt % allow for 3pt kerns on either
+        \advance\cartouter by 18.4pt % allow for 3pt kerns on either
 %                                    side, and for 6pt waste from
-%                                    each corner char
+%                                    each corner char, and rule thickness
         \normbskip=\baselineskip \normpskip=\parskip \normlskip=\lineskip
         % Flag to tell @lisp, etc., not to narrow margin.
         \let\nonarrowing=\comment