diff --git a/C/absmi.c b/C/absmi.c
index 9bec5a3c3..82010076a 100644
--- a/C/absmi.c
+++ b/C/absmi.c
@@ -1152,8 +1152,11 @@ Yap_absmi(int inp)
 #endif
 	UNLOCK(cl->ClLock);
 #if defined(YAPOR) || defined(THREADS)
-	READ_UNLOCK(PP->PRWLock);
-	PP = NULL;
+	if (PP) {
+	  /* PP would be NULL for local preds */
+	  READ_UNLOCK(PP->PRWLock);
+	  PP = NULL;
+	}
 #endif
       }
       GONext();
diff --git a/C/tracer.c b/C/tracer.c
index 2e3ddab92..3163d149e 100644
--- a/C/tracer.c
+++ b/C/tracer.c
@@ -115,6 +115,9 @@ low_level_trace(yap_low_level_port port, PredEntry *pred, CELL *args)
   /*  extern int gc_calls; */
 
   vsc_count++;
+  if (vsc_count == 395950L)
+    vsc_xstop = 1;
+  return;
 #ifdef COMMENTED
   if (port != enter_pred ||
       !pred ||