I remember that it was already discussed. I found this one: http://groups.google.de/group/comp.lang.modula3/browse_thread/thread/5b7cfe805da66f0b/7182f91c5e6e893d?hl=de&lnk=gst&q=range+check but it seems to be out of date. So once again: How can I disable checks on overflow, array bound violation, NIL pointer etc. in cm3 for the sake of speed? I hoped that '-A' (disable code generation for assertions) would do it, since these checks are like built-in ASSERTs, but I was wrong.