diff --git a/src/prolog/lib/clpb.pl b/src/prolog/lib/clpb.pl
index d66257ee..f373f83a 100644
--- a/src/prolog/lib/clpb.pl
+++ b/src/prolog/lib/clpb.pl
@@ -31,6 +31,7 @@
 :- use_module(library(atts)).
 :- use_module(library(lists)).
 :- use_module(library(iso_ext)).
+:- use_module(library(random)).
 :- use_module(library(pairs)).
 :- use_module(library(dcgs)).
 :- use_module(library(error), []).
diff --git a/src/prolog/lib/iso_ext.pl b/src/prolog/lib/iso_ext.pl
index 68708250..e206fd0b 100644
--- a/src/prolog/lib/iso_ext.pl
+++ b/src/prolog/lib/iso_ext.pl
@@ -4,10 +4,10 @@
 %% ?- use_module(library(iso_ext)).
 
 :- module(iso_ext, [bb_b_put/2, bb_get/2, bb_put/2, call_cleanup/2,
-		            call_with_inference_limit/3, forall/2, maybe/0,
-		            partial_string/1, partial_string/3,
-		            partial_string_tail/2, set_random/1,
-		            setup_call_cleanup/3, variant/2]).
+                    call_with_inference_limit/3, forall/2,
+                    partial_string/1, partial_string/3,
+                    partial_string_tail/2, setup_call_cleanup/3,
+                    variant/2]).
 
 forall(Generate, Test) :-
     \+ (Generate, \+ Test).
@@ -22,9 +22,9 @@ bb_put(Key, _) :- throw(error(type_error(atom, Key), bb_put/2)).
 bb_b_put(Key, NewValue) :-
     (  '$bb_get_with_offset'(Key, OldValue, OldOffset) ->
        call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		            reset_global_var_at_offset(Key, OldValue, OldOffset))
+                    reset_global_var_at_offset(Key, OldValue, OldOffset))
     ;  call_cleanup((store_global_var_with_offset(Key, NewValue) ; false),
-		            reset_global_var_at_key(Key))
+                    reset_global_var_at_key(Key))
     ).
 
 store_global_var_with_offset(Key, Value) :- '$store_global_var_with_offset'(Key, Value).
@@ -144,27 +144,12 @@ call_with_inference_limit(_, _, R, Bb, B) :-
 
 variant(X, Y) :- '$variant'(X, Y).
 
-% succeeds with probability 0.5.
-maybe :- '$maybe'.
-
-set_random(Seed) :-
-    (  nonvar(Seed) ->
-       (  Seed = seed(S) ->
-	  (  var(S) -> throw(error(instantiation_error, set_random/1))
-	  ;  integer(S) -> '$set_seed'(S)
-	  ;  throw(error(type_error(integer(S), set_random/1)))
-	  )
-       )
-    ;  throw(error(instantiation_error, set_random/1))
-    ).
-
-
 partial_string(String, L, L0) :-
     (  String == [] ->
        L = L0
     ;  catch(atom_chars(Atom, String),
-	     error(E, _),
-	     throw(error(E, partial_string/3))),
+         error(E, _),
+         throw(error(E, partial_string/3))),
        '$create_partial_string'(Atom, L, L0)
     ).
 
diff --git a/src/prolog/lib/random.pl b/src/prolog/lib/random.pl
new file mode 100644
index 00000000..7e59fc23
--- /dev/null
+++ b/src/prolog/lib/random.pl
@@ -0,0 +1,51 @@
+:- module(random, [maybe/0, random/1, random_integer/3, set_random/1]).
+
+% succeeds with probability 0.5.
+maybe :- '$maybe'.
+
+% The higher the precision, the slower it gets.
+random_number_precision(64).
+
+random(R) :-
+    var(R),
+    random_number_precision(N),
+    rnd(N, R).
+
+random_integer(Lower, Upper, R) :-
+    var(R),
+    (   (var(Lower) ; var(Upper)) ->
+            throw(error(instantiation_error, random_integer/3))
+    ;   \+ integer(Lower) ->
+            throw(error(domain_error(integer, Lower), random_integer/3))
+    ;   \+ integer(Upper) ->
+            throw(error(domain_error(integer, Upper), random_integer/3))
+    ;   Upper > Lower,
+        random(R0),
+        R is floor((Upper - Lower) * R0 + Lower)
+    ).
+
+rnd(N, R) :-
+    rnd_(N, 0, R).
+
+rnd_(0, R, R) :- !.
+rnd_(N, R0, R) :-
+    maybe,
+    !,
+    N1 is N - 1,
+    rnd_(N1, R0, R).
+rnd_(N, R0, R) :-
+    N1 is N - 1,
+    R1 is R0 + 1.0 / 2.0 ^ N,
+    rnd_(N1, R1, R).
+
+set_random(Seed) :-
+    (   nonvar(Seed) ->
+        (  Seed = seed(S) ->
+        (  var(S) -> throw(error(instantiation_error, set_random/1))
+        ;  integer(S) -> '$set_seed'(S)
+        ;  throw(error(type_error(integer(S), set_random/1)))
+        )
+        )
+    ;   throw(error(instantiation_error, set_random/1))
+    ).
+