diff --git a/makefiles/Mf-install.in b/makefiles/Mf-install.in
index 17489555e1..bc93bee18a 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=csv9.5.3.16
+Version=csv9.5.3.17
 Include=boot/$m
 PetiteBoot=boot/$m/petite.boot
 SchemeBoot=boot/$m/scheme.boot
diff --git a/s/cmacros.ss b/s/cmacros.ss
index a3846d7a64..73d7fad1ea 100644
--- a/s/cmacros.ss
+++ b/s/cmacros.ss
@@ -328,7 +328,7 @@
                  [(_ foo e1 e2) e1] ...
                  [(_ bar e1 e2) e2]))))])))
 
-(define-constant scheme-version #x09050310)
+(define-constant scheme-version #x09050311)
 
 (define-syntax define-machine-types
   (lambda (x)
diff --git a/s/cpnanopass.ss b/s/cpnanopass.ss
index b2dffae410..386ab39fb9 100644
--- a/s/cpnanopass.ss
+++ b/s/cpnanopass.ss
@@ -9716,6 +9716,11 @@
                [else #f])])
           (define-inline 2 $sealed-record?
             [(e e-rtd) (build-sealed-isa? e e-rtd)])
+          (define-inline 3 $record-type-field-count
+            [(e) (%inline srl ,(%inline - ,(%mref ,e ,(constant record-type-size-disp))
+                                        (immediate ,(fxsll (fx- (constant record-data-disp) (constant record-type-disp))
+                                                           (constant fixnum-offset))))
+                          ,(%constant log2-ptr-bytes))])
           (define-inline 2 eq-hashtable?
             [(e) (let ([rtd (let () (include "hashtable-types.ss") (record-type-descriptor eq-ht))])
                    (let ([e-rtd `(quote ,rtd)])
diff --git a/s/primdata.ss b/s/primdata.ss
index bc41a5e55a..0fda26e60b 100644
--- a/s/primdata.ss
+++ b/s/primdata.ss
@@ -2236,6 +2236,7 @@
   ($record-set! [sig [(ptr sub-index ptr) -> (void)]] [flags true])
   ($record-type-descriptor [flags single-valued pure mifoldable discard true])
   ($record-type-field-offsets [flags single-valued pure mifoldable discard true])
+  ($record-type-field-count [sig [(ptr) -> (fixnum)]] [flags single-valued pure mifoldable discard true])
   ($reloc [flags single-valued])
   ($remake-rtd [flags single-valued])
   ($report-string [flags single-valued])
diff --git a/s/prims.ss b/s/prims.ss
index 82c2f55fda..8e528c88f0 100644
--- a/s/prims.ss
+++ b/s/prims.ss
@@ -2054,6 +2054,12 @@
   (unless ($record? r) ($oops who "~s is not a record" r))
   (#3%$record-type-descriptor r))
 
+;; Assumes that the record that has only pointer fields:
+(define-who ($record-type-field-count rtd)
+  (unless (record-type-descriptor? rtd)
+    ($oops who "~s is not a record type descriptor" rtd))
+  ($record-type-field-count rtd))
+
 (define-who utf8->string
   (let ()
     (define slurp