diff --git a/mps/code/config.h b/mps/code/config.h
index c07f646a0af..1dfd7858f86 100644
--- a/mps/code/config.h
+++ b/mps/code/config.h
@@ -290,7 +290,7 @@
 
 /* Pool AMS Configuration -- see <code/poolams.c> */
 
-#define AMS_SUPPORT_AMBIGUOUS_DEFAULT FALSE
+#define AMS_SUPPORT_AMBIGUOUS_DEFAULT TRUE
 #define AMS_GEN_DEFAULT       0
 
 
diff --git a/mps/manual/source/pool/ams.rst b/mps/manual/source/pool/ams.rst
index cb7966661a3..ae1d43f8bed 100644
--- a/mps/manual/source/pool/ams.rst
+++ b/mps/manual/source/pool/ams.rst
@@ -55,10 +55,11 @@ AMS properties
   never promoted out of the generation in which they are allocated.
 
 * Blocks may contain :term:`exact references` to blocks in the same or
-  other pools, or :term:`ambiguous references` (if the
+  other pools, or :term:`ambiguous references` (unless the
   :c:macro:`MPS_KEY_AMS_SUPPORT_AMBIGUOUS` keyword argument is set to
-  true when creating the pool). Blocks may not contain :term:`weak
-  references (1)`, and may not use :term:`remote references`.
+  ``FALSE`` when creating the pool). Blocks may not contain
+  :term:`weak references (1)`, and may not use :term:`remote
+  references`.
 
 * Allocations may be variable in size.
 
@@ -126,14 +127,13 @@ AMS interface
       blocks remain in this generation and are not promoted.
 
     * :c:macro:`MPS_KEY_AMS_SUPPORT_AMBIGUOUS` (type
-      :c:type:`mps_bool_t`, default false) specifies whether references
-      may be ambiguous.
+      :c:type:`mps_bool_t`, default ``TRUE``) specifies whether
+      references to blocks in the pool may be ambiguous.
 
     For example::
 
         MPS_ARGS_BEGIN(args) {
             MPS_ARGS_ADD(args, MPS_KEY_FORMAT, fmt);
-            MPS_ARGS_ADD(args, MPS_KEY_AMS_SUPPORT_AMBIGUOUS, 1);
             res = mps_pool_create_k(&pool, arena, mps_class_ams(), args);
         } MPS_ARGS_END(args);
 
diff --git a/mps/manual/source/release.rst b/mps/manual/source/release.rst
index 18cc8ed72e9..f9fc0054de5 100644
--- a/mps/manual/source/release.rst
+++ b/mps/manual/source/release.rst
@@ -35,6 +35,11 @@ Interface changes
    :c:func:`mps_arena_create_k` when creating a virtual memory arena.
    See :c:func:`mps_arena_class_vm`.
 
+#. The keyword argument :c:macro:`MPS_KEY_AMS_SUPPORT_AMBIGUOUS` now
+   defaults to ``TRUE`` in order to better support the general case:
+   the value ``FALSE`` is appropriate only when you know that all
+   references are exact. See :ref:`pool-ams`.
+
 
 Other changes
 .............