[Ok, ignore all my previous ramblings....I checked FSF 20.3's source now.] Jan Vroonhof <vroonhof(a)math.ethz.ch&gt; writes: So FSF does use the glibc allocator. However Steve forced XEmacs minimal tag bit support to on when using the Doug lea allocator. I cannot remember why. FSF Emacs doesn't have minimal tag bit support doesn't it? That could be the difference but it seems to me now to be more pure luck. (XEmacs also doesn't free the malloc_state_ptr but surely that cannot be it. Just for the record: That is in an XEmacs bug. Jan