Problem getting non-blocking sockets going on BSD 2.11

I'm in the midst of writing a MUD for PDP-11s running under BSD 2.11 and have run into a problem getting non-blocking I/O working. I initially wrote a simple test program to setup a non-blocking socket and accept connections then echo back anything typed to all connected sessions. This worked fine. However now I've placed the exact same code into my MUD development, the sockets are blocking. I've got the following in my setup of the socket: /* Set socket to non-blocking */ if( ioctl(s,FIONBIO) == -1 ) { printf("Error ocurred"); } which I believe should make the socket non-block and when I run up the code it doesn't throw a failure on the ioctl, however the socket definitely remains in blocking mode. Anyone have any ideas? I've been scratching my head on this one for days now