Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c (revision 41673)
+++ channels/chan_sip.c (working copy)
@@ -10909,7 +10909,10 @@
        }

        AST_STANDARD_APP_ARGS(args, data);
-       sscanf(args.number, "%d", &number);
+       if (!args.number)
+               number = 1;
+       else
+               sscanf(args.number, "%d", &number);
        if (number < 1)
                number = 1;