Check the underside of the safety lever for the little detent nub. If it's not completely worn off, you can try either bending the safety lever toward the reciever a little bit to put more tension on the detent; you can also take a very small drill bit and drill in a new/deeper detent divot for the nub to sit in.
If the nub is gone (unlikely?), or you can't get the lever to bend, or you find any other excuse, a replacememt can be bought from any number of places.
The lever on my Saiga is actually far too stiff and doesn't move easily enough.