diff --git a/packages/ProbLog/dtproblog.yap b/packages/ProbLog/dtproblog.yap
index 5e530b498..f368e019c 100644
--- a/packages/ProbLog/dtproblog.yap
+++ b/packages/ProbLog/dtproblog.yap
@@ -408,7 +408,7 @@ set_strategy(_) :-
 set_strategy([]) :- problog_control(on,internal_strategy).
 set_strategy([Term|R]) :-
   strategy_entry(Term,LogProb,Decision),
-  (ground(Decision)->
+  (user:problog_user_ground(Decision)->
       decision_fact(ID,Decision),
       grounding_id(ID,Decision,ID2),
       %format("Setting ~q/~q to ~q~n",[Decision,ID2,Prob]),
@@ -427,7 +427,7 @@ unset_strategy([]) :-
   problog_control(off,internal_strategy).
 unset_strategy([Term|R]) :-
   strategy_entry(Term,LogProb,Decision),
-  (ground(Decision)->
+  (user:problog_user_ground(Decision)->
       decision_fact(ID,Decision),
       grounding_id(ID,Decision,ID2),
       %format("Unsetting ~q/~q to ~q~n",[Decision,ID2,Prob]),
diff --git a/packages/ProbLog/problog.yap b/packages/ProbLog/problog.yap
index b7083adcf..f7be7462e 100644
--- a/packages/ProbLog/problog.yap
+++ b/packages/ProbLog/problog.yap
@@ -2,8 +2,8 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %
-%  $Date: 2010-10-21 10:47:36 +0200 (Thu, 21 Oct 2010) $
-%  $Revision: 4970 $
+%  $Date: 2010-11-09 02:47:35 +0100 (Tue, 09 Nov 2010) $
+%  $Revision: 4991 $
 %
 %  This file is part of ProbLog
 %  http://dtai.cs.kuleuven.be/problog
@@ -881,19 +881,21 @@ problog_predicate(Name, Arity, ProblogName,Mod) :-
 % non-ground probabilistic facts
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+:- multifile(user:problog_user_ground/1).
+user:problog_user_ground(Goal) :-
+  ground(Goal).
+
 non_ground_fact_grounding_id(Goal,ID) :-
-	ground(Goal),
-	!,
-	(
-	 grounding_is_known(Goal,ID)
-	->
-	 true;
-	 (
+  user:problog_user_ground(Goal), !,
+	(grounding_is_known(Goal,ID) ->
+	  true
+	;
+	  (
 	  nb_getval(non_ground_fact_grounding_id_counter,ID),
 	  ID2 is ID+1,
 	  nb_setval(non_ground_fact_grounding_id_counter,ID2),
 	  assertz(grounding_is_known(Goal,ID))
-	 )
+	  )
 	).
 non_ground_fact_grounding_id(Goal,_) :-	
 	format(user_error,'The current program uses non-ground facts.~n', []),