diff --git a/mps/code/policy.c b/mps/code/policy.c
index 51c2ee8f110..e44f67ad9fa 100644
--- a/mps/code/policy.c
+++ b/mps/code/policy.c
@@ -265,6 +265,11 @@ Bool PolicyStartTrace(Trace *traceReturn, Bool *collectWorldReturn,
   Res res;
   Trace trace;
   double TraceWorkFactor = 0.25;
+  /* Fix the mortality of the world to avoid runaway feedback between the
+     dynamic criterion and the mortality of the arena's top generation,
+     leading to all traces collecting the world. This is a (hopefully)
+     temporary hack, pending an improved scheduling algorithm. */
+  double TraceWorldMortality = 0.5;
 
   AVER(traceReturn != NULL);
   AVERT(Arena, arena);
@@ -278,7 +283,7 @@ Bool PolicyStartTrace(Trace *traceReturn, Bool *collectWorldReturn,
     sFoundation = (Size)0; /* condemning everything, only roots @@@@ */
     /* @@@@ sCondemned should be scannable only */
     sCondemned = ArenaCommitted(arena) - ArenaSpareCommitted(arena);
-    sSurvivors = (Size)(sCondemned * (1 - arena->topGen.mortality));
+    sSurvivors = (Size)(sCondemned * (1 - TraceWorldMortality));
     tTracePerScan = sFoundation + (sSurvivors * (1 + TraceCopyScanRATIO));
     AVER(TraceWorkFactor >= 0);
     AVER(sSurvivors + tTracePerScan * TraceWorkFactor <= (double)SizeMAX);