diff --git a/src/cmp/cmpfun.lsp b/src/cmp/cmpfun.lsp
index c60a671d2..467832965 100644
--- a/src/cmp/cmpfun.lsp
+++ b/src/cmp/cmpfun.lsp
@@ -305,8 +305,8 @@
 
 (put-sysprop 'apply 'C1 'c1apply)
 
-(put-sysprop 'rplaca 'C1 'c1rplaca)
-(put-sysprop 'rplaca 'C2 'c2rplaca)
+;(put-sysprop 'rplaca 'C1 'c1rplaca)
+;(put-sysprop 'rplaca 'C2 'c2rplaca)
 (put-sysprop 'rplacd 'C1 'c1rplacd)
 (put-sysprop 'rplacd 'C2 'c2rplacd)
 
diff --git a/src/cmp/cmpopt-cons.lsp b/src/cmp/cmpopt-cons.lsp
new file mode 100644
index 000000000..7c392a39b
--- /dev/null
+++ b/src/cmp/cmpopt-cons.lsp
@@ -0,0 +1,52 @@
+;;;;  -*- Mode: Lisp; Syntax: Common-Lisp; Package: C -*-
+;;;;
+;;;;  CMPOPT-CONS  Optimization of CONS functions
+;;;;
+;;;;  Copyright (c) 2010, Juan Jose Garcia-Ripoll
+;;;;
+;;;;    This program is free software; you can redistribute it and/or
+;;;;    modify it under the terms of the GNU Library General Public
+;;;;    License as published by the Free Software Foundation; either
+;;;;    version 2 of the License, or (at your option) any later version.
+;;;;
+;;;;    See file '../Copyright' for full details.
+
+(in-package "COMPILER")
+
+(defun expand-simple-optimizer (values arg-types inline-form env)
+  `(ffi:c-inline ,(if (policy-assume-right-type env)
+                      values
+                      (loop for v in values
+                         for value-and-type in arg-types
+                         collect (if (consp value-and-type)
+                                     `(assert-type-if-known ,v ,(second value-and-type))
+                                     v)))
+                 ,@inline-form))
+
+(defun simple-optimizer-function (name args inline-form)
+  (si::put-sysprop
+   name 'si::compiler-macro
+   (if (every #'symbolp args)
+       #'(lambda (whole env)
+           (if (policy-inline-accessors env)
+               `(ffi:c-inline ,(rest whole) ,@inline-form)
+               whole))
+       #'(lambda (whole env)
+           (if (policy-inline-accessors env)
+               (expand-simple-optimizer (rest whole) args inline-form env)
+               whole)))))
+
+;;;
+;;; RPLACA / RPLACD
+;;;
+
+(defmacro define-simple-optimizer (name args &rest inline-form)
+  `(simple-optimizer-function ',name ',args ',inline-form))
+
+(define-simple-optimizer rplaca ((c cons) value)
+  (:object :object) :object
+  "ECL_CONS_CAR(#0)=#1" :one-liner t)
+
+(define-simple-optimizer rplacd ((c cons) value)
+  (:object :object) :object
+  "ECL_CONS_CDR(#0)=#1" :one-liner t)
diff --git a/src/cmp/load.lsp.in b/src/cmp/load.lsp.in
index e62863819..6d98461d6 100644
--- a/src/cmp/load.lsp.in
+++ b/src/cmp/load.lsp.in
@@ -45,6 +45,7 @@
   "src:cmp;cmpnum.lsp"
   "src:cmp;cmpname.lsp"
   "src:cmp;cmpopt.lsp"
+  "src:cmp;cmpopt-cons.lsp"
   "src:cmp;cmpprop.lsp"
   "src:cmp;cmpclos.lsp"
   "src:cmp;cmpstructures.lsp"