diff --git a/mps/src/buffer.c b/mps/src/buffer.c
index 0b99980e5c4..056f65badd1 100644
--- a/mps/src/buffer.c
+++ b/mps/src/buffer.c
@@ -1,6 +1,6 @@
 /* impl.c.buffer: ALLOCATION BUFFER IMPLEMENTATION
  *
- * $HopeName: MMsrc!buffer.c(trunk.55) $
+ * $HopeName: MMsrc!buffer.c(trunk.56) $
  * Copyright (C) 1999.  Harlequin Limited.  All rights reserved.
  *
  * .purpose: This is (part of) the implementation of allocation buffers.
@@ -22,7 +22,7 @@
 
 #include "mpm.h"
 
-SRCID(buffer, "$HopeName: MMsrc!buffer.c(trunk.55) $");
+SRCID(buffer, "$HopeName: MMsrc!buffer.c(trunk.56) $");
 
 
 /* forward declarations */
@@ -1370,7 +1370,7 @@ static Res segBufInit (Buffer buffer, Pool pool, va_list args)
   segbuf = BufferSegBuf(buffer);
 
   /* Initialize the superclass fields first via next-method call */
-  super = EnsureBufferClass();
+  super = BUFFER_SUPERCLASS(SegBufClass);
   res = super->init(buffer, pool, args);
   if (res != ResOK)
     return res;
@@ -1398,7 +1398,7 @@ static void segBufFinish (Buffer buffer)
   segbuf->sig = SigInvalid;
 
   /* finish the superclass fields last */
-  super = EnsureBufferClass();
+  super = BUFFER_SUPERCLASS(SegBufClass);
   super->finish(buffer);
 }
 
@@ -1534,7 +1534,7 @@ static Res segBufDescribe(Buffer buffer, mps_lib_FILE *stream)
     return ResFAIL;
 
   /* Describe the superclass fields first via next-method call */
-  super = EnsureBufferClass();
+  super = BUFFER_SUPERCLASS(SegBufClass);
   res = super->describe(buffer, stream);
   if(res != ResOK)
     return res;
@@ -1592,7 +1592,7 @@ static Res rankBufInit (Buffer buffer, Pool pool, va_list args)
   AVER(RankCheck(rank));
 
   /* Initialize the superclass fields first via next-method call */
-  super = EnsureSegBufClass();
+  super = BUFFER_SUPERCLASS(RankBufClass);
   res = super->init(buffer, pool, args);
   if (res != ResOK)
     return res;
diff --git a/mps/src/mpm.h b/mps/src/mpm.h
index c29b5b94e47..fa5c3b0bf69 100644
--- a/mps/src/mpm.h
+++ b/mps/src/mpm.h
@@ -1,6 +1,6 @@
 /* impl.h.mpm: MEMORY POOL MANAGER DEFINITIONS
  *
- * $HopeName: MMsrc!mpm.h(trunk.128) $
+ * $HopeName: MMsrc!mpm.h(trunk.129) $
  * Copyright (C) 1999.  Harlequin Limited.  All rights reserved.
  */
 
@@ -441,6 +441,9 @@ extern AbstractCollectPoolClass EnsureAbstractCollectPoolClass(void);
 #define DEFINE_POOL_CLASS(className, var) \
   DEFINE_ALIAS_CLASS(className, PoolClass, var)
 
+#define POOL_SUPERCLASS(className) \
+  (PoolClass)SUPERCLASS(className)
+
 
 /* Message Interface -- see design.mps.message */
 
@@ -612,6 +615,9 @@ extern void ActionPoll(Arena arena);
 #define DEFINE_ARENA_CLASS(className, var) \
   DEFINE_ALIAS_CLASS(className, ArenaClass, var)
 
+#define ARENA_SUPERCLASS(className) \
+  (ArenaClass)SUPERCLASS(className)
+
 extern AbstractArenaClass EnsureAbstractArenaClass(void);
 extern Bool ArenaClassCheck(ArenaClass class);
 extern Bool ArenaCheck(Arena arena);
@@ -830,6 +836,9 @@ extern void SegClassMixInNoSplitMerge(SegClass class);
 #define DEFINE_SEG_CLASS(className, var) \
   DEFINE_ALIAS_CLASS(className, SegClass, var)
 
+#define SEG_SUPERCLASS(className) \
+  (SegClass)SUPERCLASS(className)
+
 extern Size SegSize(Seg seg);
 extern Addr (SegBase)(Seg seg);
 extern Addr (SegLimit)(Seg seg);
@@ -934,6 +943,8 @@ extern void BufferFrameSetState(Buffer buffer, FrameState state);
 #define DEFINE_BUFFER_CLASS(className, var) \
   DEFINE_ALIAS_CLASS(className, BufferClass, var)
 
+#define BUFFER_SUPERCLASS(className) \
+  (BufferClass)SUPERCLASS(className)
 
 extern Bool BufferClassCheck(BufferClass class);
 extern BufferClass EnsureBufferClass(void);