diff --git a/mps/src/misc.h b/mps/src/misc.h
index b13696fd535..6aada6e092e 100644
--- a/mps/src/misc.h
+++ b/mps/src/misc.h
@@ -1,7 +1,7 @@
 /* impl.h.misc: MISCELLANEOUS DEFINITIONS
  *
- * $HopeName: MMsrc!misc.h(trunk.18) $
- * Copyright (C) 1997 The Harlequin Group Limited.  All rights reserved.
+ * $HopeName: MMsrc!misc.h(trunk.19) $
+ * Copyright (C) 1997. Harlequin Group plc. All rights reserved.
  *
  * Small general things which are useful for C but aren't part of the
  * memory manager itself.  The only reason that this file exists is
@@ -119,6 +119,7 @@ typedef const struct SrcIdStruct {
 #define BS_EMPTY(ty)            ((ty)0)
 #define BS_COMP(s)              (~(s))
 #define BS_UNIV(ty)             BS_COMP(BS_EMPTY(ty))
+#define BS_UPPER_HALF(ty)       (BS_UNIV(ty) << (sizeof(ty) * 4))
 #define BS_SINGLE(ty, i)        ((ty)1 << (i))
 #define BS_IS_MEMBER(s, i)      (((s) >> (i)) & 1)
 #define BS_UNION(s1, s2)        ((s1) | (s2))