diff --git a/mps/code/amcss.c b/mps/code/amcss.c
index b284379394e..ba4a3bfc7c2 100644
--- a/mps/code/amcss.c
+++ b/mps/code/amcss.c
@@ -301,7 +301,7 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, 2*testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 15));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(2*testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args), "arena_create");
   } MPS_ARGS_END(args);
   mps_message_type_enable(arena, mps_message_type_gc());
diff --git a/mps/code/amcsshe.c b/mps/code/amcsshe.c
index 1fc9345140e..ced80bcc0cf 100644
--- a/mps/code/amcsshe.c
+++ b/mps/code/amcsshe.c
@@ -249,7 +249,7 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, 2*testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 15));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(2*testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args), "arena_create");
   } MPS_ARGS_END(args);
   mps_message_type_enable(arena, mps_message_type_gc());
diff --git a/mps/code/amcssth.c b/mps/code/amcssth.c
index 38a349c3778..f4dedd55f7f 100644
--- a/mps/code/amcssth.c
+++ b/mps/code/amcssth.c
@@ -319,7 +319,7 @@ static void test_arena(int mode)
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 14));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args), "arena_create");
   } MPS_ARGS_END(args);
   if (mode == ModeCOMMIT)
diff --git a/mps/code/amsss.c b/mps/code/amsss.c
index 3fdf1ef55aa..915c8ed1522 100644
--- a/mps/code/amsss.c
+++ b/mps/code/amsss.c
@@ -208,7 +208,7 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 14));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args), "arena_create");
   } MPS_ARGS_END(args);
   die(mps_arena_commit_limit_set(arena, 2 * testArenaSIZE), "commit_limit_set");
diff --git a/mps/code/amssshe.c b/mps/code/amssshe.c
index edac9733149..26dc25822e5 100644
--- a/mps/code/amssshe.c
+++ b/mps/code/amssshe.c
@@ -163,7 +163,7 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 14));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args), "arena_create");
   } MPS_ARGS_END(args);
   die(mps_thread_reg(&thread, arena), "thread_reg");
diff --git a/mps/code/apss.c b/mps/code/apss.c
index 4bd4f203aa4..7de122af10d 100644
--- a/mps/code/apss.c
+++ b/mps/code/apss.c
@@ -204,7 +204,7 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, 2 * testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 20));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(2*testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args),
         "mps_arena_create");
   } MPS_ARGS_END(args);
@@ -215,7 +215,7 @@ int main(int argc, char *argv[])
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, 2 * testArenaSIZE);
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_ZONED, FALSE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 20));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(2*testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_vm(), args),
         "mps_arena_create");
   } MPS_ARGS_END(args);
@@ -226,7 +226,7 @@ int main(int argc, char *argv[])
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, testArenaSIZE);
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_ZONED, FALSE);
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_CL_BASE, malloc(testArenaSIZE));
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 20));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(testArenaSIZE));
     die(mps_arena_create_k(&arena, mps_arena_class_cl(), args),
         "mps_arena_create");
   } MPS_ARGS_END(args);
diff --git a/mps/code/mpmss.c b/mps/code/mpmss.c
index a069c2f8a48..e3914be9d93 100644
--- a/mps/code/mpmss.c
+++ b/mps/code/mpmss.c
@@ -219,13 +219,13 @@ int main(int argc, char *argv[])
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, testArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 20));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(testArenaSIZE));
     testInArena(mps_arena_class_vm(), args, &bothOptions);
   } MPS_ARGS_END(args);
 
   MPS_ARGS_BEGIN(args) {
     MPS_ARGS_ADD(args, MPS_KEY_ARENA_SIZE, smallArenaSIZE);
-    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, (size_t)1 << (rnd() % 15));
+    MPS_ARGS_ADD(args, MPS_KEY_ARENA_GRAIN_SIZE, rnd_grain(smallArenaSIZE));
     testInArena(mps_arena_class_vm(), args, &fenceOptions);
   } MPS_ARGS_END(args);
 
diff --git a/mps/code/testlib.c b/mps/code/testlib.c
index 6ecedad0bd6..5aa4a2f4e4e 100644
--- a/mps/code/testlib.c
+++ b/mps/code/testlib.c
@@ -12,7 +12,7 @@
 #include "mps.h"
 #include "misc.h" /* for NOOP */
 
-#include <math.h> /* fmod */
+#include <math.h> /* fmod, log2 */
 #include <stdio.h> /* fflush, printf, stderr, sscanf, vfprintf */
 #include <stdlib.h> /* abort, exit, getenv */
 #include <time.h> /* time */
@@ -220,6 +220,14 @@ double rnd_double(void)
   return rnd() / R_m_float;
 }
 
+size_t rnd_grain(size_t arena_size)
+{
+  /* The grain size must be small enough to allow for a complete set
+   * of zones in the initial chunk. */
+  size_t s = (size_t)log2((double)arena_size);
+  Insist(s > MPS_WORD_SHIFT);
+  return (size_t)1 << (rnd() % (s - MPS_WORD_SHIFT));
+}
 
 rnd_state_t rnd_seed(void)
 {
diff --git a/mps/code/testlib.h b/mps/code/testlib.h
index 38a4c94bdab..edeaf5eb50b 100644
--- a/mps/code/testlib.h
+++ b/mps/code/testlib.h
@@ -248,6 +248,12 @@ extern mps_addr_t rnd_addr(void);
 extern double rnd_double(void);
 
 
+/* rnd_grain -- return a random grain size that's not too big for the
+ * given arena size */
+
+extern size_t rnd_grain(size_t arena_size);
+
+
 /* randomize -- randomize the generator, or initialize to replay
  *
  * randomize(argc, argv) randomizes the rnd generator (using time(3))
diff --git a/mps/manual/source/mmref-index.rst b/mps/manual/source/mmref-index.rst
index c645899bb49..a91b7b702c4 100644
--- a/mps/manual/source/mmref-index.rst
+++ b/mps/manual/source/mmref-index.rst
@@ -6,7 +6,7 @@ Welcome to the **Memory Management Reference**!  This is a resource for programm
 
 .. admonition:: :ref:`glossary`
 
-    A glossary of more than 500 memory management terms, from
+    A glossary of more than 500 :term:`memory management` terms, from
     :term:`absolute address` to :term:`zero count table`.
 
     .. image:: diagrams/treadmill.svg
@@ -17,7 +17,8 @@ Welcome to the **Memory Management Reference**!  This is a resource for programm
 
 .. admonition:: :ref:`mmref-intro`
 
-    Articles giving a beginner's overview of memory management.
+    Articles giving a beginner's overview of :term:`memory
+    management`.
 
     .. image:: diagrams/address.svg
         :target: intro_
@@ -27,7 +28,7 @@ Welcome to the **Memory Management Reference**!  This is a resource for programm
 
 .. admonition:: :ref:`bibliography`
 
-    Books and research papers related to memory management.
+    Books and research papers related to :term:`memory management`.
 
     .. image:: diagrams/copying.svg
         :target: bib_
@@ -37,7 +38,7 @@ Welcome to the **Memory Management Reference**!  This is a resource for programm
 
 .. admonition:: :ref:`mmref-faq`
 
-    Frequently asked questions about memory management.
+    Frequently asked questions about :term:`memory management`.
 
     .. image:: diagrams/snap-out.svg
         :target: faq_
@@ -46,9 +47,9 @@ Welcome to the **Memory Management Reference**!  This is a resource for programm
 
 The Memory Management Reference is maintained by `Ravenbrook
 Limited`_. We also maintain the `Memory Pool System`_ (an open-source,
-thread-safe, :term:`incremental <incremental garbage collection>`
-garbage collector), and we are happy to provide advanced memory
-management solutions to language and application developers through
+thread-safe, :term:`incremental garbage collector <incremental garbage
+collection>`), and we are happy to provide advanced :term:`memory
+management` solutions to language and application developers through
 our `consulting service`_.
 
 .. _Ravenbrook Limited: http://www.ravenbrook.com/
diff --git a/mps/manual/source/release.rst b/mps/manual/source/release.rst
index c739f46ad9c..c025ad75a40 100644
--- a/mps/manual/source/release.rst
+++ b/mps/manual/source/release.rst
@@ -47,9 +47,9 @@ Interface changes
 .................
 
 #. The granularity with which the arena manages memory can now be
-   specified using the :c:macro:`MPS_KEY_ARENA_SIZE` keyword argument
-   to :c:func:`mps_arena_create_k`. See :c:func:`mps_arena_class_cl`
-   and :c:func:`mps_arena_class_vm`.
+   specified using the :c:macro:`MPS_KEY_ARENA_GRAIN_SIZE` keyword
+   argument to :c:func:`mps_arena_create_k`. See
+   :c:func:`mps_arena_class_cl` and :c:func:`mps_arena_class_vm`.
 
 #. There is now a default value (currently 256 \ :term:`megabytes`)
    for the :c:macro:`MPS_KEY_ARENA_SIZE` keyword argument to