diff --git a/doc/tex/misdn.tex b/doc/tex/misdn.tex
index 9ac245ebf7..2d5c9413c8 100644
--- a/doc/tex/misdn.tex
+++ b/doc/tex/misdn.tex
@@ -122,7 +122,7 @@ so the generic dial string looks like:
 
 \begin{astlisting}
 \begin{verbatim}
-mISDN/<port>|g:<group>/<extension>[/<OPTIONSSTRING>]
+mISDN/<port>[:bchannel]|g:<group>/<extension>[/<OPTIONSSTRING>]
 
 The Optionsstring looks Like:
 :<optchar><optarg>:<optchar><optarg>...