diff --git a/mps/code/cbs.c b/mps/code/cbs.c
index 4a6169895d1..842bb4cfb9d 100644
--- a/mps/code/cbs.c
+++ b/mps/code/cbs.c
@@ -70,7 +70,6 @@ Bool CBSCheck(CBS cbs)
   CHECKL(SplayTreeCheck(splayTreeOfCBS(cbs)));
   /* nothing to check about splayTreeSize */
   CHECKD(Pool, cbs->blockPool);
-  CHECKU(Arena, cbs->arena);
   CHECKL(BoolCheck(cbs->fastFind));
   CHECKL(BoolCheck(cbs->inCBS));
   CHECKL(BoolCheck(cbs->ownPool));
@@ -170,9 +169,7 @@ static void cbsUpdateNode(SplayTree tree, SplayNode node,
                           SplayNode leftChild, SplayNode rightChild)
 {
   Size maxSize;
-  ZoneSet zones;
   CBSBlock block;
-  Arena arena;
 
   AVERT(SplayTree, tree);
   AVERT(SplayNode, node);
@@ -184,25 +181,20 @@ static void cbsUpdateNode(SplayTree tree, SplayNode node,
 
   block = cbsBlockOfSplayNode(node);
   maxSize = CBSBlockSize(block);
-  arena = cbsOfSplayTree(tree)->arena;
-  zones = ZoneSetOfRange(arena, CBSBlockBase(block), CBSBlockLimit(block));
 
   if (leftChild != NULL) {
     Size size = cbsBlockOfSplayNode(leftChild)->maxSize;
     if (size > maxSize)
       maxSize = size;
-    zones = ZoneSetUnion(zones, cbsBlockOfSplayNode(leftChild)->zones);
   }
 
   if (rightChild != NULL) {
     Size size = cbsBlockOfSplayNode(rightChild)->maxSize;
     if (size > maxSize)
       maxSize = size;
-    zones = ZoneSetUnion(zones, cbsBlockOfSplayNode(rightChild)->zones);
   }
 
   block->maxSize = maxSize;
-  block->zones = zones;
 }
 
 
@@ -232,7 +224,6 @@ Res CBSInit(Arena arena, CBS cbs, void *owner, Align alignment,
   if (ArgPick(&arg, args, MFSExtendSelf))
     extendSelf = arg.val.b;
 
-  cbs->arena = arena;
   SplayTreeInit(splayTreeOfCBS(cbs), &cbsSplayCompare,
                 fastFind ? &cbsUpdateNode : NULL);
 
@@ -819,20 +810,6 @@ static Bool cbsTestNodeInZones(SplayTree tree, SplayNode node,
                         closure->arena, closure->zoneSet, closure->size);
 }
 
-static Bool cbsTestTreeInZones(SplayTree tree, SplayNode node,
-                               void *closureP, Size closureSize)
-{
-  CBSBlock block = cbsBlockOfSplayNode(node);
-  cbsTestNodeInZonesClosure closure = closureP;
-  
-  UNUSED(tree);
-  AVER(closureSize == sizeof(cbsTestNodeInZonesClosureStruct));
-  UNUSED(closureSize);
-  
-  return block->maxSize >= closure->size &&
-         ZoneSetInter(block->zones, closure->zoneSet) != ZoneSetEMPTY;
-}
-
 Bool CBSFindFirstInZones(Range rangeReturn, Range oldRangeReturn,
                          CBS cbs, Size size,
                          Arena arena, ZoneSet zoneSet)
@@ -874,7 +851,7 @@ Bool CBSFindFirstInZones(Range rangeReturn, Range oldRangeReturn,
   closure.size = size;
   found = SplayFindFirst(&node, splayTreeOfCBS(cbs),
                          &cbsTestNodeInZones,
-                         &cbsTestTreeInZones,
+                         &cbsTestTree,
                          &closure, sizeof(closure));
   if (found) {
     CBSBlock block = cbsBlockOfSplayNode(node);
diff --git a/mps/code/mpmst.h b/mps/code/mpmst.h
index a0154f8d7bf..ddffdf60570 100644
--- a/mps/code/mpmst.h
+++ b/mps/code/mpmst.h
@@ -615,7 +615,6 @@ typedef struct CBSStruct {
   SplayTreeStruct splayTree;
   STATISTIC_DECL(Count splayTreeSize);
   Pool blockPool;
-  Arena arena;                  /* needed by update method */
   Align alignment;
   Bool fastFind;
   Bool inCBS;                   /* prevent reentrance */