diff --git a/src/pl-trace.c b/src/pl-trace.c
index ae69b7364f..5db944a784 100644
--- a/src/pl-trace.c
+++ b/src/pl-trace.c
@@ -112,7 +112,7 @@ PL_put_frame(term_t t, LocalFrame fr)
 }
 
 
-static int
+static bool
 PL_get_frame(term_t r, LocalFrame *fr)
 { GET_LD
   intptr_t i;
@@ -121,18 +121,16 @@ PL_get_frame(term_t r, LocalFrame *fr)
   if ( PL_get_intptr(r, &i) )
   { LocalFrame f = ((LocalFrame)((Word)lBase + i));
 
-    if ( !(f >= lBase && f < lTop) )
-      fail;
-    *fr = f;
-
-    succeed;
+    if ( existingFrame(f) )
+    { *fr = f;
+      return true;
+    }
   } else if ( PL_get_atom(r, &a) && a == ATOM_none )
   { *fr = NULL;
-
-    succeed;
+    return true;
   }
 
-  fail;
+  return false;
 }
 
 
@@ -149,7 +147,7 @@ PL_put_choice(term_t t, Choice ch)
 }
 
 
-static int
+static bool
 PL_unify_choice(term_t t, Choice ch)
 { GET_LD
 
@@ -163,7 +161,7 @@ PL_unify_choice(term_t t, Choice ch)
 
 
 #define valid_choice(ch) LDFUNC(valid_choice, ch)
-static inline int
+static inline bool
 valid_choice(DECL_LD Choice ch)
 { if ( (int)ch->type >= 0 && (int)ch->type <= CHP_DEBUG &&
        onStack(local, ch->frame) )
@@ -173,12 +171,12 @@ valid_choice(DECL_LD Choice ch)
 }
 
 
-static int
+static bool
 PL_get_choice(term_t r, Choice *chp)
 { GET_LD
-  long i;
+  intptr_t i;
 
-  if ( PL_get_long(r, &i) )
+  if ( PL_get_intptr(r, &i) )
   { Choice ch = ((Choice)((Word)lBase + i));
 
     if ( !(ch >= (Choice)lBase && ch < (Choice)lTop) ||
@@ -186,7 +184,7 @@ PL_get_choice(term_t r, Choice *chp)
       return PL_error(NULL, 0, NULL, ERR_EXISTENCE, ATOM_choice, r);
     *chp = ch;
 
-    succeed;
+    return true;
   } else
     return PL_error(NULL, 0, NULL, ERR_TYPE, ATOM_choice, r);
 }
@@ -200,7 +198,7 @@ tracer. `No-debug' code has HIDE_CHILDS. Calls to  it must be visible if
 the parent is a debug frame.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-int
+bool
 isDebugFrame(LocalFrame FR)
 { if ( isoff(FR->predicate, TRACE_ME) )
     return false;			/* hidden predicate */
@@ -224,7 +222,7 @@ isDebugFrame(LocalFrame FR)
   } else
   { QueryFrame qf = queryOfFrame(FR);
 
-    return (qf->flags & PL_Q_NODEBUG) ? false : true;
+    return !(qf->flags & PL_Q_NODEBUG);
   }
 }
 
@@ -1782,8 +1780,8 @@ interruptHandler(int sig)
 
     if ( (ex=PL_new_term_ref()) &&
 	 PL_unify_term(ex, PL_FUNCTOR, FUNCTOR_unwind1,
-		             PL_FUNCTOR, FUNCTOR_thread_exit1,
-		               PL_ATOM, ATOM_true) )
+			     PL_FUNCTOR, FUNCTOR_thread_exit1,
+			       PL_ATOM, ATOM_true) )
       return;
   }
 #endif
diff --git a/src/pl-trace.h b/src/pl-trace.h
index ba2c8fd8f9..f0c0e13edf 100644
--- a/src/pl-trace.h
+++ b/src/pl-trace.h
@@ -52,7 +52,7 @@
 #define LDFUNC_DECLARATIONS
 
 void		suspendTrace(int suspend);	/* suspend/resume tracing */
-int		isDebugFrame(LocalFrame FR);
+bool		isDebugFrame(LocalFrame FR);
 int		tracePort(LocalFrame frame, Choice bfr,
 			  int port, Code PC);
 void		initTracer(void);
diff --git a/src/pl-wam.c b/src/pl-wam.c
index c4b730e888..5b12a78625 100644
--- a/src/pl-wam.c
+++ b/src/pl-wam.c
@@ -2521,7 +2521,7 @@ chp_chars(Choice ch)
 #endif
 
 
-int
+bool
 existingChoice(DECL_LD Choice ch)
 { if ( onStack(local, ch) && onStack(local, ch->frame) &&
        (int)ch->type >= 0 && (int)ch->type <= CHP_DEBUG )
@@ -2537,6 +2537,24 @@ existingChoice(DECL_LD Choice ch)
 }
 
 
+bool
+existingFrame(DECL_LD LocalFrame fr)
+{ for(;;)
+  { if ( !onStack(local, fr) )
+      return false;
+    if ( !isFrame(fr) )
+      return false;
+
+    if ( fr->parent )
+    { fr = fr->parent;
+    } else
+    { QueryFrame qf = queryOfFrame(fr);
+      return qf->magic == QID_MAGIC;
+    }
+  }
+}
+
+
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 discardChoicesAfter() discards all choicepoints created  after fr, while
 calling  possible  hooks  on   the   frames.    If   the   `reason`   is
diff --git a/src/pl-wam.h b/src/pl-wam.h
index ffa29d2499..5210c8010f 100644
--- a/src/pl-wam.h
+++ b/src/pl-wam.h
@@ -52,6 +52,7 @@
 #define	PL_next_solution(qid)		LDFUNC(PL_next_solution, qid)
 #define	foreignWakeup(ex)		LDFUNC(foreignWakeup, ex)
 #define	existingChoice(ch)		LDFUNC(existingChoice, ch)
+#define	existingFrame(fr)		LDFUNC(existingFrame, fr)
 #define grow_trail_ptr(p)		LDFUNC(grow_trail_ptr, p)
 #define handles_unwind(qid, flags)	LDFUNC(handles_unwind, qid, flags)
 #endif /*USE_LD_MACROS*/
@@ -76,7 +77,8 @@ bool		raiseSignal(PL_local_data_t *ld, int sig);
 int		pendingSignal(PL_local_data_t *ld, int sig);
 Module		contextModule(LocalFrame fr);
 void		setContextModule(LocalFrame fr, Module context);
-int		existingChoice(Choice ch);
+bool		existingChoice(Choice ch);
+bool		existingFrame(LocalFrame fr);
 int		grow_trail_ptr(Word p);
 bool		handles_unwind(qid_t qid, unsigned int flags);
 #ifdef O_DEBUG