diff --git a/doc/scsh-manual/miscprocs.tex b/doc/scsh-manual/miscprocs.tex
index 2aa5a80..5b8e2cd 100644
--- a/doc/scsh-manual/miscprocs.tex
+++ b/doc/scsh-manual/miscprocs.tex
@@ -372,6 +372,8 @@ C library written by Colin Plum.
 \defun{md5-digest-for-port}{port [buffer-size]}{md5-digest}
 \begin{desc}
   Reads the contents of the port and calculates the MD5 digest for it.
+  The optional argument \var{buffer-size} determines the size of the
+  port's input buffer in bytes. It defaults to 1024 bytes.
 \end{desc}
 
 \defun{md5-digest?}{thing}{boolean}