diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index c060c8d676b..d8dbfa62bf9 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -1410,13 +1410,14 @@ See Info node `(elisp) Integer Basics'."
       form)))
 
 (defun byte-optimize-not (form)
-  (and (= (length form) 2)
-       (let ((arg (nth 1 form)))
-         (cond ((null arg) t)
-               ((macroexp-const-p arg) nil)
-               ((byte-compile-nilconstp arg) `(progn ,arg t))
-               ((byte-compile-trueconstp arg) `(progn ,arg nil))
-               (t form)))))
+  (if (= (length form) 2)
+      (let ((arg (nth 1 form)))
+        (cond ((null arg) t)
+              ((macroexp-const-p arg) nil)
+              ((byte-compile-nilconstp arg) `(progn ,arg t))
+              ((byte-compile-trueconstp arg) `(progn ,arg nil))
+              (t form)))
+    form))
 
 (put 'and   'byte-optimizer #'byte-optimize-and)
 (put 'or    'byte-optimizer #'byte-optimize-or)