diff --git a/lib/chibi/optional-test.sld b/lib/chibi/optional-test.sld
index 66d6b342..d90c6337 100644
--- a/lib/chibi/optional-test.sld
+++ b/lib/chibi/optional-test.sld
@@ -73,6 +73,11 @@
         (let-optionals* ls ((a (begin (set! ls '(a b)) 'default-a))
                             (b 'default-b))
           (test '(default-a default-b) (list a b))))
+      (let ((ls (list 0 1 2)))
+        (let-optionals ls (a . b)
+          (set-car! (cdr ls) 3)
+          (test '(0 3 2) ls)
+          (test '(0 1 2) (cons a b))))
       (test 5 (keyword-ref '(a: b: b: 5) 'b: #f))
       (test 5 (keyword-ref* '(a: b: b: 5) 'b: #f))
       (cond-expand
diff --git a/lib/chibi/optional.scm b/lib/chibi/optional.scm
index c30158c2..abbe3c15 100644
--- a/lib/chibi/optional.scm
+++ b/lib/chibi/optional.scm
@@ -76,7 +76,7 @@
 (define-syntax opt-lambda
   (syntax-rules ()
     ((opt-lambda vars . body)
-     (opt-lambda/aux let-optionals () vars . body))))
+     (lambda args (let-optionals args vars . body)))))
 
 ;;> \macro{(opt-lambda* ((var default) ... [rest]) body ...)}
 ;;>
@@ -86,18 +86,7 @@
 (define-syntax opt-lambda*
   (syntax-rules ()
     ((opt-lambda* vars . body)
-     (opt-lambda/aux let-optionals* () vars . body))))
-
-(define-syntax opt-lambda/aux
-  (syntax-rules ()
-    ((opt-lambda/aux let-opt (args ...) ((var . default) . vars) . body)
-     (lambda (args ... . o)
-       (let-opt o ((var . default) . vars) . body)))
-    ((opt-lambda/aux let-opt (args ...) (var . vars) . body)
-     (opt-lambda/aux let-opt (args ... var) vars . body))
-    ((opt-lambda/aux let-op (args ...) () . body)
-     (lambda (args ... . o)
-       . body))))
+     (lambda args (let-optionals* args vars . body)))))
 
 ;;> \macro{(define-opt (name (var default) ... [rest]) body ...)}
 ;;>
diff --git a/lib/chibi/optional.sld b/lib/chibi/optional.sld
index 98033be0..4368042d 100644
--- a/lib/chibi/optional.sld
+++ b/lib/chibi/optional.sld
@@ -36,7 +36,7 @@
                   (var (if (pair? tmp) (car tmp) default)))
              (let-optionals* tmp2 rest . body)))
           ((let-optionals* tmp tail . body)
-           (let ((tail tmp)) . body))))
+           (let ((tail (list-copy tmp))) . body))))
       (define-syntax symbol->keyword*
         (syntax-rules ()
           ((symbol->keyword* sym)
diff --git a/lib/init-7.scm b/lib/init-7.scm
index 9b1d662f..d6507367 100644
--- a/lib/init-7.scm
+++ b/lib/init-7.scm
@@ -1146,7 +1146,7 @@
      (let ((var (car tmp)))
        (let-optionals* (cdr tmp) rest . body)))
     ((let-optionals* tmp tail . body)
-     (let ((tail tmp)) . body))))
+     (let ((tail (list-copy tmp))) . body))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; exceptions