diff --git a/mps/code/cbs.c b/mps/code/cbs.c
index addebd398ad..3e3411023eb 100644
--- a/mps/code/cbs.c
+++ b/mps/code/cbs.c
@@ -232,14 +232,11 @@ static void cbsUpdateZonedNode(SplayTree splay, Tree tree)
  * See <design/cbs/#function.cbs.init>.
  */
 
-ARG_DEFINE_KEY(cbs_extend_by, Size);
 ARG_DEFINE_KEY(cbs_block_pool, Pool);
 
 Res CBSInit(CBS cbs, Arena arena, void *owner, Align alignment,
             Bool fastFind, Bool zoned, ArgList args)
 {
-  Size extendBy = CBS_EXTEND_BY_DEFAULT;
-  Bool extendSelf = TRUE;
   ArgStruct arg;
   Res res;
   Pool blockPool = NULL;
@@ -253,10 +250,6 @@ Res CBSInit(CBS cbs, Arena arena, void *owner, Align alignment,
 
   if (ArgPick(&arg, args, CBSBlockPool))
     blockPool = arg.val.pool;
-  if (ArgPick(&arg, args, MPS_KEY_CBS_EXTEND_BY))
-    extendBy = arg.val.size;
-  if (ArgPick(&arg, args, MFSExtendSelf))
-    extendSelf = arg.val.b;
 
   update = SplayTrivUpdate;
   if (fastFind)
@@ -274,8 +267,6 @@ Res CBSInit(CBS cbs, Arena arena, void *owner, Align alignment,
   } else {
     MPS_ARGS_BEGIN(pcArgs) {
       MPS_ARGS_ADD(pcArgs, MPS_KEY_MFS_UNIT_SIZE, sizeof(CBSBlockStruct));
-      MPS_ARGS_ADD(pcArgs, MPS_KEY_EXTEND_BY, extendBy);
-      MPS_ARGS_ADD(pcArgs, MFSExtendSelf, extendSelf);
       res = PoolCreate(&cbs->blockPool, arena, PoolClassMFS(), pcArgs);
     } MPS_ARGS_END(pcArgs);
     if (res != ResOK)
diff --git a/mps/code/config.h b/mps/code/config.h
index 1dfd7858f86..5d2eff42104 100644
--- a/mps/code/config.h
+++ b/mps/code/config.h
@@ -264,11 +264,6 @@
 #define BUFFER_RANK_DEFAULT (mps_rank_exact())
 
 
-/* CBS Configuration -- see <code/cbs.c> */
-
-#define CBS_EXTEND_BY_DEFAULT ((Size)4096)
-
-
 /* Format defaults: see <code/format.c> */
 
 #define FMT_ALIGN_DEFAULT ((Align)MPS_PF_ALIGN)
diff --git a/mps/code/mps.h b/mps/code/mps.h
index 18767cec60f..049a489f96d 100644
--- a/mps/code/mps.h
+++ b/mps/code/mps.h
@@ -188,9 +188,6 @@ extern const struct mps_key_s _mps_key_max_size;
 extern const struct mps_key_s _mps_key_align;
 #define MPS_KEY_ALIGN           (&_mps_key_align)
 #define MPS_KEY_ALIGN_FIELD     align
-extern const struct mps_key_s _mps_key_cbs_extend_by;
-#define MPS_KEY_CBS_EXTEND_BY   (&_mps_key_cbs_extend_by)
-#define MPS_KEY_CBS_EXTEND_BY_FIELD size
 extern const struct mps_key_s _mps_key_interior;
 #define MPS_KEY_INTERIOR        (&_mps_key_interior)
 #define MPS_KEY_INTERIOR_FIELD  b