diff --git a/module/system/vm/assemble.scm b/module/system/vm/assemble.scm
index 5987f1cda..acdcbe3ca 100644
--- a/module/system/vm/assemble.scm
+++ b/module/system/vm/assemble.scm
@@ -173,6 +173,7 @@
 			    (lambda (obj+index)
 			      (cond ((cdr obj+index) =>
 				     (lambda (n)
+				       (push-code! '(dup))
 				       (push-code! `(local-set ,n)))))))))
 		   (push-code! (car stack)))))
 	   ;; closures
diff --git a/src/vm_system.c b/src/vm_system.c
index 97ac41e41..ba31f74ae 100644
--- a/src/vm_system.c
+++ b/src/vm_system.c
@@ -70,7 +70,8 @@ VM_DEFINE_INSTRUCTION (drop, "drop", 0, 0, 0)
 
 VM_DEFINE_INSTRUCTION (dup, "dup", 0, 0, 1)
 {
-  PUSH (*sp);
+  SCM x = *sp;
+  PUSH (x);
   NEXT;
 }