Just crashed gprolog

Hi there,

I'm trying to learn prolog,
and built myself a small ancestor file which follows:

-----8<----------------- z.pl

parent(francis,odile).
parent(marcelle,odile).
parent(germaine,bernard).
parent(marcel,bernard).
parent(bernard,manu).
parent(odile,manu).
parent(manu,leo).
parent(jolene,leo).

ancestor(X,Y) :- parent(X,Y).
ancestor(X,Y) :- ancestor(X,Z), ancestor(Z,Y).

-----8<----------------- z.pl


I then launch gprolog, and here's what happens:

marune #./gprolog.exe
GNU Prolog 1.2.16
By Daniel Diaz
Copyright (C) 1999-2002 Daniel Diaz
| ?- [z].
compiling /usr/gprolog-1.2.16/bin/z.pl for byte code...
/usr/gprolog-1.2.16/bin/z.pl compiled, 13 lines read - 1337 bytes written, 120 ms

yes
| ?- ancestor(X,leo).

X = manu ? ;

X = jolene ? ;

X = francis ? ;
Segmentation fault (core dumped)


Am I doing something wrong ?

Is the tree of ancestors that huge that I'm
causing the unification to fail ?