diff --git a/doc/misdn.txt b/doc/misdn.txt
index 1870eb0910..bb119feaaf 100644
--- a/doc/misdn.txt
+++ b/doc/misdn.txt
@@ -135,7 +135,7 @@ Dial and Options String
 The dial string of chan_misdn got more complex, because we added more features,
 so the generic dial string looks like:
 
-mISDN/<port>|g:<group>/<extension>[/<OPTIONSSTRING>]
+mISDN/<port>[:bchannel]|g:<group>/<extension>[/<OPTIONSSTRING>]
 
 The Optionsstring looks Like:
 :<optchar><optarg>:<optchar><optarg>...