diff --git a/mps/src/mpm.c b/mps/src/mpm.c
index 0ca80e07c89..a8921302c8e 100644
--- a/mps/src/mpm.c
+++ b/mps/src/mpm.c
@@ -1,6 +1,6 @@
 /* impl.c.mpm: GENERAL MPM SUPPORT
  *
- * $HopeName: MMsrc!mpm.c(trunk.25) $
+ * $HopeName: MMsrc!mpm.c(trunk.26) $
  * Copyright (C) 1996.  Harlequin Group plc.  All rights reserved.
  *
  * .readership: MM developers.
@@ -17,7 +17,7 @@
 #include <float.h>
 
 
-SRCID(mpm, "$HopeName: MMsrc!mpm.c(trunk.25) $");
+SRCID(mpm, "$HopeName: MMsrc!mpm.c(trunk.26) $");
 
 
 /* MPMCheck -- test MPM assumptions */
@@ -140,6 +140,25 @@ Word (WordAlignUp)(Word word, Align align)
   return WordAlignUp(word, align);
 }
 
+/* WordRoundUp -- round word up to round.
+ *
+ * .wordroundup.arg.word: the quantity to be rounded.
+ * .wordroundup.arg.round: The modulus to round to.  Not necessarily
+ *   an alignment (ie not a power of two).
+ *
+ * .wordroundup.result:
+ * Let m be congruent to 0 mod r (m == 0(r)),
+ *   and let m be the least m >= w.
+ * If w+r-1 (!) is representible in Word then result is m.
+ * Otherwise result is 0.  Wittily.
+ * (NB result may be 0 even if m is representible)
+ */
+Word (WordRoundUp)(Word word, Size round)
+{
+  AVER(round > 0);
+  return WordRoundUp(word, round);
+}
+
 
 /* WordAlignUp -- round a word down to the nearest aligned value */
 
diff --git a/mps/src/mpm.h b/mps/src/mpm.h
index 434c86521d2..122b52da946 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.99) $
+ * $HopeName: MMsrc!mpm.h(trunk.100) $
  * Copyright (C) 1998.  Harlequin Group plc.  All rights reserved.
  */
 
@@ -50,6 +50,10 @@ extern Bool (WordIsAligned)(Word word, Align align);
 extern Word (WordAlignUp)(Word word, Align align);
 #define WordAlignUp(w, a)       (((w) + (a) - 1) & ~((Word)(a) - 1))
 
+/* Rounds w up to a multiple of r, see impl.c.mpm for exact behaviour */
+extern Word (WordRoundUp)(Word word, Size round);
+#define WordRoundUp(w, r)       (((w)+(r)-1) - ((w)+(r)-1)%(r))
+
 extern Word (WordAlignDown)(Word word, Align align);
 #define WordAlignDown(w, a)     ((w) & ~((Word)(a) - 1))
 
@@ -90,6 +94,10 @@ extern Addr (AddrAlignDown)(Addr addr, Align align);
 #define SizeAlignUp(s, a)       ((Size)WordAlignUp(SizeWord(s), (a)))
 #define SizeAlignDown(s, a)     ((Size)WordAlignDown(SizeWord(s), (a)))
 
+/* r not required to be a power of 2 */
+#define SizeRoundUp(s, r) \
+  ((Size)WordRoundUp(SizeWord(s), (Size)(r)))
+
 extern Addr (AddrSet)(Addr target, Byte value, Size size);
 /* This is one of the places that implements Addr, so it's allowed to */
 /* convert to void *, see design.mps.type.addr.ops.mem. */