diff -Nru cl-nibbles-20201208.git8e6b9b4/debian/changelog cl-nibbles-20210520.gitdad2524/debian/changelog
--- cl-nibbles-20201208.git8e6b9b4/debian/changelog	2020-12-17 09:25:28.000000000 +0000
+++ cl-nibbles-20210520.gitdad2524/debian/changelog	2021-08-26 18:36:29.000000000 +0000
@@ -1,3 +1,11 @@
+cl-nibbles (20210520.gitdad2524-1) unstable; urgency=medium
+
+  * New upstream snapshot
+    Fixes amd64 autopkgtest against sbcl 2:2.1.7-1.
+  * Bump to S-V 4.6.0
+
+ -- Sébastien Villemot <sebastien@debian.org>  Thu, 26 Aug 2021 20:36:29 +0200
+
 cl-nibbles (20201208.git8e6b9b4-1) unstable; urgency=medium
 
   * New upstream snapshot
diff -Nru cl-nibbles-20201208.git8e6b9b4/debian/control cl-nibbles-20210520.gitdad2524/debian/control
--- cl-nibbles-20201208.git8e6b9b4/debian/control	2020-12-04 10:31:00.000000000 +0000
+++ cl-nibbles-20210520.gitdad2524/debian/control	2021-08-26 18:36:02.000000000 +0000
@@ -4,7 +4,7 @@
 Maintainer: Debian Common Lisp Team <debian-common-lisp@lists.debian.org>
 Uploaders: Sébastien Villemot <sebastien@debian.org>
 Build-Depends: debhelper-compat (= 13)
-Standards-Version: 4.5.1
+Standards-Version: 4.6.0
 Rules-Requires-Root: no
 Homepage: https://github.com/sharplispers/nibbles
 Vcs-Git: https://salsa.debian.org/common-lisp-team/cl-nibbles.git
diff -Nru cl-nibbles-20201208.git8e6b9b4/sbcl-opt/x86-64-vm.lisp cl-nibbles-20210520.gitdad2524/sbcl-opt/x86-64-vm.lisp
--- cl-nibbles-20201208.git8e6b9b4/sbcl-opt/x86-64-vm.lisp	2020-12-08 23:06:19.000000000 +0000
+++ cl-nibbles-20210520.gitdad2524/sbcl-opt/x86-64-vm.lisp	2021-05-20 19:51:26.000000000 +0000
@@ -64,14 +64,26 @@
                   (result-sc (if signedp 'signed-reg 'unsigned-reg))
                   (result-type (if signedp 'signed-num 'unsigned-num)))
              (flet ((movx (insn dest source source-size)
-                      (if (eq insn 'mov)
-                          `(inst ,insn ,dest ,source)
-                          `(inst ,(case insn (movsxd 'movsx) (movzxd 'movzx) (t insn))
-                                 '(,source-size :qword) ,dest ,source)))
+                      (cond ((eq insn 'mov)
+                             `(inst ,insn ,dest ,source))
+                            ;; (movzx (:dword :qword) dest source) is
+                            ;; no longer allowed on SBCL > 2.1.4.134
+                            ;; but older versions already supported
+                            ;; this new spelling.
+                            ((and (member insn '(movzx movzxd))
+                                  (eq source-size :dword))
+                             `(inst mov :dword ,dest ,source))
+                            (t
+                             `(inst ,(case insn (movsxd 'movsx) (movzxd 'movzx) (t insn))
+                                    '(,source-size :qword) ,dest ,source))))
                     (swap-tn-inst-form (tn-name)
                       (if (= bitsize 16)
                           `(inst rol ,operand-size ,tn-name 8)
-                          `(inst bswap ,operand-size ,tn-name))))
+                          ;; The '(bswap :dword r)' notation is only
+                          ;; supported on SBCL > 1.5.9.
+                          (if (ignore-errors (sb-ext:assert-version->= 1 5 9 17) t)
+                              `(inst bswap ,operand-size ,tn-name)
+                              `(inst bswap (sb-vm::reg-in-size ,tn-name ,operand-size))))))
                `(define-vop (,name)
                   (:translate ,internal-name)
                   (:policy :fast-safe)