diff --git a/csug/threads.stex b/csug/threads.stex
index e964a78f3d..c495006b7f 100644
--- a/csug/threads.stex
+++ b/csug/threads.stex
@@ -568,6 +568,36 @@ allocation of the containing object and decremented upon freeing
 of the containing object.
 
 
+
+\section{Memory Consistency\label{SECTSMGMTMEMMODEL}}
+
+Scheme threads can expose the memory-consistency model of the
+underlying processor, except to the degree that it would interefere
+with the memory safety of Scheme programs. For example, if two threads
+share a vector, then a \scheme{vector-set!} in one thread will not
+allow the other thread to read the vector and see a partially
+constructed primitive object installed into the vector; the Scheme
+system includes a memory fence around operations and on platforms as
+needed to preserve safety. There's no guarantee, for example, that
+assigning to multiple slots in an fxvector will become visible in the
+same order to other threads that share the vector, because no such
+ordering is required to preserve memory safety.
+
+%----------------------------------------------------------------------------
+\entryheader
+\formdef{memory-order-acquire}{\categoryprocedure}{(memory-order-acquire)}
+\formdef{memory-order-release}{\categoryprocedure}{(memory-order-release)}
+\returns unspecified
+\listlibraries
+\endnoskipentryheader
+
+These procedures fence memory operations in a way that is consistent
+with acquire--release patterns. Specifically,
+\scheme{memory-order-acquire} ensures at least a load--load and
+load--store fence, and \scheme{memory-order-release} ensures at least
+a store--store and store--load fence.
+
+
 \section{Thread Parameters\label{SECTTHREADPARAMETERS}}
 
 %----------------------------------------------------------------------------
diff --git a/makefiles/Mf-install.in b/makefiles/Mf-install.in
index 9ce6714100..71bb66cee5 100644
--- a/makefiles/Mf-install.in
+++ b/makefiles/Mf-install.in
@@ -62,7 +62,7 @@ InstallLZ4Target=
 #                 no changes should be needed below this point                #
 ###############################################################################
 
-Version=csv9.5.3.31
+Version=csv9.5.3.32
 Include=boot/$m
 PetiteBoot=boot/$m/petite.boot
 SchemeBoot=boot/$m/scheme.boot
diff --git a/mats/thread.ms b/mats/thread.ms
index 9c361330d7..64d9e403d0 100644
--- a/mats/thread.ms
+++ b/mats/thread.ms
@@ -1568,6 +1568,51 @@
         (set! done? #t)
         (condition-broadcast c))
       (equal? gc-ids (list (get-thread-id)))))
+  )
+
+(mat memory-consistency
+  (equal? (memory-order-acquire) (void))
+  (equal? (memory-order-release) (void))
+  ;; Try to make a thread see a partially constructed box
+  (let ([ids '(one two three four)])
+    (let ([m (make-mutex)]
+          [c (make-condition)]
+          [ok? #t]
+          [running (length ids)]
+          [v (make-vector 1000 (box (car ids)))])
+      (let loop ([i running])
+        (unless (= i 0)
+          (fork-thread (lambda ()
+                         (let ([id (list-ref ids (sub1 i))]
+                               [failed? #f])
+                           (let loop ([j 10000])
+                             (cond
+                               [(fx= j 0)
+                                (mutex-acquire m)
+                                (set! running (sub1 running))
+                                (condition-signal c)
+                                (set! ok? (and ok? (not failed?)))
+                                (mutex-release m)]
+                               [else
+                                (let loop ([i 0])
+                                  (unless (fx= i (vector-length v))
+                                    (let ([b (vector-ref v i)])
+                                      (unless (and (box? b)
+                                                   (memq (unbox b) ids))
+                                        (set! failed? #t)))
+                                    (vector-set! v i (box id))
+                                    (loop (fx+ i 1))))
+                                (loop (fx- j 1))])))))
+          (loop (sub1 i))))
+      (mutex-acquire m)
+      (let loop ()
+        (cond
+          [(not (zero? running))
+           (condition-wait c m)
+           (loop)]
+          [else
+           (mutex-release m)]))
+      ok?))
 )
 
 (mat wait-for-threads
@@ -1581,6 +1626,6 @@
           (sleep (make-time 'time-duration 10000 0))
           (loop))))
     #t)
-)  
+)
 
 )
diff --git a/s/arm32.ss b/s/arm32.ss
index a2d61ee040..53321e3d36 100644
--- a/s/arm32.ss
+++ b/s/arm32.ss
@@ -985,9 +985,17 @@
                `(set! ,(make-live-info) ,u2 (asm ,null-info ,asm-kill))
 	       `(asm ,info ,asm-cas ,r ,old ,new ,u1 ,u2)))))]))
 
-  (define-instruction effect (write-write-fence)
+  (define-instruction effect (store-store-fence)
     [(op)
-     `(asm ,info ,asm-write-write-fence)])
+     `(asm ,info ,(asm-fence 'store-store))])
+
+  (define-instruction effect (acquire-fence)
+    [(op)
+     `(asm ,info ,(asm-fence 'acquire))])
+  
+  (define-instruction effect (release-fence)
+    [(op)
+     `(asm ,info ,(asm-fence 'release))])
 
   (define-instruction effect (pause)
     ; NB: user sqrt or something like that?
@@ -1033,7 +1041,7 @@
                      asm-rp-header asm-rp-compact-header
                      asm-indirect-call asm-condition-code
                      asm-fpmove-single asm-fl-cvt asm-fpt asm-fpmove asm-fpcastto asm-fpcastfrom asm-fptrunc 
-                     asm-lock asm-lock+/- asm-cas asm-write-write-fence
+                     asm-lock asm-lock+/- asm-cas asm-fence
                      asm-fpop-2 asm-fpsqrt asm-c-simple-call
                      asm-save-flrv asm-restore-flrv asm-return asm-c-return asm-size
                      asm-enter asm-foreign-call asm-foreign-callable
@@ -1186,7 +1194,9 @@
   (define-op ldrex ldrex-op      #b00011001)
   (define-op strex strex-op      #b00011000)
 
-  (define-op dmbst dmb-op #b1110)
+  (define-op dmbst    dmb-op #b1110)
+  (define-op dmbish   dmb-op #b1011)
+  (define-op dmbishst dmb-op #b1010)
 
   (define-op bnei  branch-imm-op       (ax-cond 'ne))
   (define-op brai  branch-imm-op       (ax-cond 'al))
@@ -2182,9 +2192,15 @@
                 (emit cmpi tmp2 0
                    code*))))))))
 
-  (define asm-write-write-fence
-    (lambda (code*)
-      (emit dmbst code*)))
+  ;; Based in part on https://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html
+  (define-who asm-fence
+    (lambda (kind)
+      (lambda (code*)
+        (case kind
+          [(store-store) (emit dmbishst code*)]
+          [(acquire) (emit dmbish code*)]
+          [(release) (emit dmbish code*)]
+          [else (sorry! who "unexpected kind ~s" kind)]))))
 
   (define asm-fp-relop
     (lambda (info)
diff --git a/s/arm64.ss b/s/arm64.ss
index bcf4341c40..119ab1944f 100644
--- a/s/arm64.ss
+++ b/s/arm64.ss
@@ -822,9 +822,17 @@
                `(set! ,(make-live-info) ,u2 (asm ,null-info ,asm-kill))
 	       `(asm ,info ,asm-cas ,r ,old ,new ,u1 ,u2)))))]))
 
-  (define-instruction effect (write-write-fence)
+  (define-instruction effect (store-store-fence)
     [(op)
-     `(asm ,info ,asm-write-write-fence)])
+     `(asm ,info ,(asm-fence 'store-store))])
+
+  (define-instruction effect (acquire-fence)
+    [(op)
+     `(asm ,info ,(asm-fence 'acquire))])
+
+  (define-instruction effect (release-fence)
+    [(op)
+     `(asm ,info ,(asm-fence 'release))])
 
   (define-instruction effect (pause)
     ;; NB: use sqrt or something like that?
@@ -870,7 +878,7 @@
                      asm-rp-header asm-rp-compact-header
                      asm-indirect-call asm-condition-code
                      asm-fpmove-single asm-fl-cvt asm-fpt asm-fpmove asm-fpcastto asm-fpcastfrom asm-fptrunc 
-                     asm-lock asm-lock+/- asm-cas asm-write-write-fence
+                     asm-lock asm-lock+/- asm-cas asm-fence
                      asm-fpop-2 asm-fpsqrt asm-c-simple-call
                      asm-return asm-c-return asm-size
                      asm-enter asm-foreign-call asm-foreign-callable
@@ -1062,7 +1070,10 @@
   (define-op ldxr   ldxr-op      #b1 `(reg . ,%real-zero))
   (define-op stxr   ldxr-op      #b0)
 
-  (define-op dmbst  dmb-op #b1110)
+  (define-op dmbst    dmb-op #b1110)
+  (define-op dmbish   dmb-op #b1011)
+  (define-op dmbishld dmb-op #b1001)
+  (define-op dmbishst dmb-op #b1010)
 
   (define-op bnei  branch-imm-op       (ax-cond 'ne))
   (define-op beqi  branch-imm-op       (ax-cond 'eq))
@@ -2105,9 +2116,15 @@
                 (emit cmpi tmp2 0
                    code*))))))))
 
-  (define asm-write-write-fence
-    (lambda (code*)
-      (emit dmbst code*)))
+  ;; Based in part on https://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html
+  (define-who asm-fence
+    (lambda (kind)
+      (lambda (code*)
+        (case kind
+          [(store-store) (emit dmbishst code*)]
+          [(acquire) (emit dmbishld code*)]
+          [(release) (emit dmbish code*)]
+          [else (sorry! who "unexpected kind ~s" kind)]))))
 
   (define asm-fp-relop
     (lambda (info)
diff --git a/s/cmacros.ss b/s/cmacros.ss
index ef99a6e9e1..b720830810 100644
--- a/s/cmacros.ss
+++ b/s/cmacros.ss
@@ -348,7 +348,7 @@
 ;; ---------------------------------------------------------------------
 ;; Version and machine types:
 
-(define-constant scheme-version #x0905031F)
+(define-constant scheme-version #x09050320)
 
 (define-syntax define-machine-types
   (lambda (x)
diff --git a/s/cpnanopass.ss b/s/cpnanopass.ss
index d451d3f8e6..ea88226b37 100644
--- a/s/cpnanopass.ss
+++ b/s/cpnanopass.ss
@@ -3702,11 +3702,13 @@
               ,(%inline sll ,e
                  (immediate ,(fx- (constant char-data-offset) (constant fixnum-offset))))
               ,(%constant type-char))))
-	(define add-write-fence
+	(define add-store-fence
+          ;; A store--store fence should be good enough for safety on a platform that
+          ;; orders load dependencies (which is anything except Alpha)
 	  (lambda (e)
             (if-feature pthreads
 	      (constant-case architecture
-	        [(arm32 arm64) `(seq ,(%inline write-write-fence) ,e)]
+	        [(arm32 arm64) `(seq ,(%inline store-store-fence) ,e)]
                 [else e])
               e)))
         (define build-dirty-store
@@ -3714,8 +3716,8 @@
             [(base offset e) (build-dirty-store base %zero offset e)]
             [(base index offset e) (build-dirty-store base index offset e
                                      (lambda (base index offset e) `(set! ,(%mref ,base ,index ,offset) ,e))
-                                     (lambda (s r) (add-write-fence `(seq ,s ,r))))]
-            [(base index offset e build-assign build-seq)
+                                     (lambda (s r) (add-store-fence `(seq ,s ,r))))]
+            [(base index offset e build-assign build-barrier-seq)
              (if (nanopass-case (L7 Expr) e
                    [(quote ,d) (ptr->imm d)]
                    [else #f])
@@ -3731,13 +3733,13 @@
                        (bind #f ([e e])
                          ; eval a second so the address is not live across any calls
                          (bind #t ([a a])
-                           (build-seq
+                           (build-barrier-seq
                              (build-assign a %zero 0 e)
                              (%inline remember ,a))))
                        (bind #t ([e e])
                          ; eval a second so the address is not live across any calls
                          (bind #t ([a a])
-			   (build-seq
+			   (build-barrier-seq
                              (build-assign a %zero 0 e)
                              `(if ,(%type-check mask-fixnum type-fixnum ,e)
                                   ,(%constant svoid)
@@ -3750,7 +3752,7 @@
                 (inline ,(make-info-condition-code 'eq? #f #t) ,%condition-code)))))
         (define build-cas-seq
           (lambda (cas remember)
-	    (add-write-fence
+	    (add-store-fence
              `(if ,cas
                   (seq ,remember ,(%constant strue))
                   ,(%constant sfalse)))))
@@ -6121,6 +6123,18 @@
         (define-inline 3 $set-symbol-hash!
           ; no need for dirty store---e2 should be a fixnum
           [(e1 e2) `(set! ,(%mref ,e1 ,(constant symbol-hash-disp)) ,e2)])
+        (define-inline 2 memory-order-acquire
+          [() (if-feature pthreads
+                (constant-case architecture
+	          [(arm32 arm64) (%seq ,(%inline acquire-fence) (quote ,(void)))]
+                  [else `(quote ,(void))])
+                `(quote ,(void)))])
+        (define-inline 2 memory-order-release
+          [() (if-feature pthreads
+                (constant-case architecture
+	          [(arm32 arm64) (%seq ,(%inline release-fence) (quote ,(void)))]
+                  [else `(quote ,(void))])
+                `(quote ,(void)))])
         (let ()
           (define-syntax define-tlc-parameter
             (syntax-rules ()
diff --git a/s/np-languages.ss b/s/np-languages.ss
index 80a50a59b0..169371e7d0 100644
--- a/s/np-languages.ss
+++ b/s/np-languages.ss
@@ -563,7 +563,9 @@
   (declare-primitive push-fpmultiple effect #f) ; arm64
   (declare-primitive pop-fpmultiple effect #f) ; arm64
   (declare-primitive cas effect #f)
-  (declare-primitive write-write-fence effect #f)
+  (declare-primitive store-store-fence effect #f)
+  (declare-primitive acquire-fence effect #f)
+  (declare-primitive release-fence effect #f)
   
   (declare-primitive < pred #t)
   (declare-primitive <= pred #t)
diff --git a/s/primdata.ss b/s/primdata.ss
index bd187df1fe..182cde33fa 100644
--- a/s/primdata.ss
+++ b/s/primdata.ss
@@ -1504,6 +1504,8 @@
   (maybe-compile-file [sig [(pathname) (pathname pathname) -> (void)]] [flags true])
   (maybe-compile-library [sig [(pathname) (pathname pathname) -> (void)]] [flags true])
   (maybe-compile-program [sig [(pathname) (pathname pathname) -> (void)]] [flags true])
+  (memory-order-acquire [sig [() -> (void)]] [flags true])
+  (memory-order-release [sig [() -> (void)]] [flags true])
   (merge [sig [(procedure list list) -> (list)]] [flags true])
   (merge! [sig [(procedure list list) -> (list)]] [flags true])
   (mkdir [sig [(pathname) (pathname sub-uint) -> (void)]] [flags])
diff --git a/s/prims.ss b/s/prims.ss
index 856f5853bd..2cf077a0e7 100644
--- a/s/prims.ss
+++ b/s/prims.ss
@@ -1167,6 +1167,14 @@
         ($top-level-bound? s)
         ($oops '$top-level-bound? "~s is not a symbol" s))))
 
+(define memory-order-acquire
+  (lambda ()
+    (memory-order-acquire)))
+
+(define memory-order-release
+  (lambda ()
+    (memory-order-release)))
+
 (define-who $bignum-length
   (lambda (n)
     (unless (bignum? n) ($oops who "~s is not a bignum" n))