diff --git a/Doc/lib/libmailbox.tex b/Doc/lib/libmailbox.tex
index 9047a616c81..a142d4844fe 100644
--- a/Doc/lib/libmailbox.tex
+++ b/Doc/lib/libmailbox.tex
@@ -86,8 +86,8 @@ messages start with the EOOH line and end with a line containing only
 
 \subsection{Mailbox Objects \label{mailbox-objects}}
 
-All implementations of Mailbox objects have one externally visible
-method:
+All implementations of Mailbox objects are iterator objects, and so
+have one externally visible method:
 
 \begin{methoddesc}[mailbox]{next}{}
 Return the next message in the mailbox, created with the optional