diff --git a/C/exec.c b/C/exec.c
index 13c1298c4..0c45810f5 100644
--- a/C/exec.c
+++ b/C/exec.c
@@ -262,7 +262,7 @@ copy_execn_to_heap(Functor f, CELL *pt, unsigned int n, unsigned int arity, Term
       *H++ = pt[i];
     }
     for (i=0; i< n; i++) {
-      *H++ = h0[i-n];
+      *H++ = h0[(int)(i-n)];
     }
     tf = AbsPair(h0);
   } else {
@@ -271,7 +271,7 @@ copy_execn_to_heap(Functor f, CELL *pt, unsigned int n, unsigned int arity, Term
       *H++ = pt[i];
     }
     for (i=0; i< n; i++) {
-      *H++ = h0[i-n];
+      *H++ = h0[(int)(i-n)];
     }
     tf = AbsAppl(h0);
   }
@@ -326,7 +326,6 @@ do_execute_n(Term t, Term mod, unsigned int n)
   if (IsExtensionFunctor(f)) {
     return CallError(TYPE_ERROR_CALLABLE, mod);
   }
-  arity = ArityOfFunctor(f);
     
   if (PRED_GOAL_EXPANSION_ALL) {
     LOCK(SignalLock);
@@ -384,9 +383,9 @@ EnterCreepMode(Term t, Term mod) {
   }
   PredCreep = RepPredProp(PredPropByFunc(FunctorCreep,1));
   if (mod) {
-    ARG1 = MkPairTerm(mod,ARG1);
+    ARG1 = MkPairTerm(mod,t);
   } else {
-    ARG1 = MkPairTerm(TermProlog,ARG1);
+    ARG1 = MkPairTerm(TermProlog,t);
   }
   LOCK(SignalLock);
   CreepFlag = CalculateStackGap();
diff --git a/changes-5.1.html b/changes-5.1.html
index 425727307..4946a7dfc 100644
--- a/changes-5.1.html
+++ b/changes-5.1.html
@@ -17,6 +17,8 @@ xb
 
 <h2>Yap-5.1.3:</h2>
 <ul>
+<li> FIXED: make sure we return to system mode on failing yesno.</li>
+<li> FIXED: debugger was broken on call/n.</li>
 <li> FIXED: user:expand_goal should be called before import,
   not after.</li>
 <li> NEW: add apply SWI library to apply_macros.</li>
diff --git a/pl/boot.yap b/pl/boot.yap
index d4d67478e..c31c1cea4 100644
--- a/pl/boot.yap
+++ b/pl/boot.yap
@@ -497,7 +497,8 @@ true :- true.
 	 ),
 	 fail.
  '$yes_no'(_,_) :-
-         '$out_neg_answer'.
+	 '$enter_system_mode',
+	 '$out_neg_answer'.
 
 '$add_env_and_fail' :- fail.
 
@@ -513,7 +514,7 @@ true :- true.
  '$do_yes_no'(G, M) :-
          '$exit_system_mode',
 	 '$execute'(M:G),
-         ( '$enter_system_mode' ; '$exit_system_mode', fail ).    
+         ( '$enter_system_mode' ; '$exit_system_mode', fail).
 
  '$write_query_answer_true'([]) :- !,
 	 format(user_error,'~ntrue',[]).