diff --git a/eval.c b/eval.c
index 5d42e74d..86422e4e 100644
--- a/eval.c
+++ b/eval.c
@@ -986,7 +986,8 @@ static void generate_opcode_app (sexp ctx, sexp app) {
     emit_word(ctx, (sexp_uint_t)op);
     break;
   case SEXP_OPC_TYPE_PREDICATE:
-  case SEXP_OPC_ACCESSOR:
+  case SEXP_OPC_GETTER:
+  case SEXP_OPC_SETTER:
   case SEXP_OPC_CONSTRUCTOR:
     emit(ctx, sexp_opcode_code(op));
     if ((sexp_opcode_class(op) != SEXP_OPC_CONSTRUCTOR)
@@ -2421,22 +2422,26 @@ sexp sexp_make_constructor (sexp ctx, sexp name, sexp type) {
                           sexp_make_fixnum(type_size), NULL);
 }
 
-sexp sexp_make_accessor (sexp ctx, sexp name, sexp type, sexp index, sexp code) {
-  if (! sexp_fixnump(type))
-    return sexp_type_exception(ctx, "make-accessor: bad type", type);
+sexp sexp_make_getter (sexp ctx, sexp name, sexp type, sexp index) {
+  if ((! sexp_fixnump(type))  || (sexp_unbox_fixnum(type) < 0))
+    return sexp_type_exception(ctx, "make-getter: bad type", type);
   if ((! sexp_fixnump(index)) || (sexp_unbox_fixnum(index) < 0))
-    return sexp_type_exception(ctx, "make-accessor: bad index", index);
+    return sexp_type_exception(ctx, "make-getter: bad index", index);
   return
-    sexp_make_opcode(ctx, name, sexp_make_fixnum(SEXP_OPC_ACCESSOR), code,
-                     sexp_make_fixnum(sexp_unbox_fixnum(code)==SEXP_OP_SLOT_REF?1:2),
-                     SEXP_ZERO, type, SEXP_ZERO, SEXP_ZERO, type, index, NULL);
+    sexp_make_opcode(ctx, name, sexp_make_fixnum(SEXP_OPC_GETTER),
+                     sexp_make_fixnum(SEXP_OP_SLOT_REF), SEXP_ONE, SEXP_ZERO,
+                     type, SEXP_ZERO, SEXP_ZERO, type, index, NULL);
 }
 
-sexp sexp_make_getter (sexp ctx, sexp name, sexp type, sexp index) {
-  return sexp_make_accessor(ctx, name, type, index, sexp_make_fixnum(SEXP_OP_SLOT_REF));
-}
 sexp sexp_make_setter (sexp ctx, sexp name, sexp type, sexp index) {
-  return sexp_make_accessor(ctx, name, type, index, sexp_make_fixnum(SEXP_OP_SLOT_SET));
+  if ((! sexp_fixnump(type))  || (sexp_unbox_fixnum(type) < 0))
+    return sexp_type_exception(ctx, "make-setter: bad type", type);
+  if ((! sexp_fixnump(index)) || (sexp_unbox_fixnum(index) < 0))
+    return sexp_type_exception(ctx, "make-setter: bad index", index);
+  return
+    sexp_make_opcode(ctx, name, sexp_make_fixnum(SEXP_OPC_SETTER),
+                     sexp_make_fixnum(SEXP_OP_SLOT_SET), SEXP_TWO, SEXP_ZERO,
+                     type, SEXP_ZERO, SEXP_ZERO, type, index, NULL);
 }
 
 #endif
diff --git a/include/chibi/eval.h b/include/chibi/eval.h
index 2337feb4..437aaa37 100644
--- a/include/chibi/eval.h
+++ b/include/chibi/eval.h
@@ -40,7 +40,8 @@ enum sexp_opcode_classes {
   SEXP_OPC_ARITHMETIC_CMP,
   SEXP_OPC_IO,
   SEXP_OPC_CONSTRUCTOR,
-  SEXP_OPC_ACCESSOR,
+  SEXP_OPC_GETTER,
+  SEXP_OPC_SETTER,
   SEXP_OPC_PARAMETER,
   SEXP_OPC_FOREIGN,
   SEXP_OPC_NUM_OP_CLASSES
diff --git a/opcodes.c b/opcodes.c
index 8267f396..8e1dbeb1 100644
--- a/opcodes.c
+++ b/opcodes.c
@@ -17,16 +17,16 @@
 #define _PARAM(n, a, t) _OP(SEXP_OPC_PARAMETER, SEXP_OP_NOOP, 0, 3, t, 0, 0, n, a, 0)
 
 static struct sexp_struct opcodes[] = {
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_CAR, 1, 0, SEXP_PAIR, 0, 0, "car", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_SET_CAR, 2, 0, SEXP_PAIR, 0, 0, "set-car!", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_CDR, 1, 0, SEXP_PAIR, 0, 0, "cdr", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_SET_CDR, 2, 0, SEXP_PAIR, 0, 0, "set-cdr!", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_VECTOR_REF,2,0, SEXP_VECTOR, SEXP_FIXNUM, 0,"vector-ref", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_VECTOR_SET,3,0, SEXP_VECTOR, SEXP_FIXNUM, 0,"vector-set!", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_VECTOR_LENGTH,1,0, SEXP_VECTOR, 0, 0,"vector-length", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_STRING_REF,2,0, SEXP_STRING, SEXP_FIXNUM, 0,"string-ref", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_STRING_SET,3,0, SEXP_STRING, SEXP_FIXNUM, 0,"string-set!", 0, NULL),
-_OP(SEXP_OPC_ACCESSOR, SEXP_OP_STRING_LENGTH,1,0, SEXP_STRING, 0, 0,"string-length", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_CAR, 1, 0, SEXP_PAIR, 0, 0, "car", 0, NULL),
+_OP(SEXP_OPC_SETTER, SEXP_OP_SET_CAR, 2, 0, SEXP_PAIR, 0, 0, "set-car!", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_CDR, 1, 0, SEXP_PAIR, 0, 0, "cdr", 0, NULL),
+_OP(SEXP_OPC_SETTER, SEXP_OP_SET_CDR, 2, 0, SEXP_PAIR, 0, 0, "set-cdr!", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_VECTOR_REF,2,0, SEXP_VECTOR, SEXP_FIXNUM, 0,"vector-ref", 0, NULL),
+_OP(SEXP_OPC_SETTER, SEXP_OP_VECTOR_SET,3,0, SEXP_VECTOR, SEXP_FIXNUM, 0,"vector-set!", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_VECTOR_LENGTH,1,0, SEXP_VECTOR, 0, 0,"vector-length", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_STRING_REF,2,0, SEXP_STRING, SEXP_FIXNUM, 0,"string-ref", 0, NULL),
+_OP(SEXP_OPC_SETTER, SEXP_OP_STRING_SET,3,0, SEXP_STRING, SEXP_FIXNUM, 0,"string-set!", 0, NULL),
+_OP(SEXP_OPC_GETTER, SEXP_OP_STRING_LENGTH,1,0, SEXP_STRING, 0, 0,"string-length", 0, NULL),
 _OP(SEXP_OPC_GENERIC, SEXP_OP_FIX2FLO, 1, 0, 0, 0, 0, "exact->inexact", 0, NULL),
 _OP(SEXP_OPC_GENERIC, SEXP_OP_FLO2FIX, 1, 0, 0, 0, 0, "inexact->exact", 0, NULL),
 _OP(SEXP_OPC_GENERIC, SEXP_OP_CHAR2INT, 1, 0, SEXP_CHAR, 0, 0, "char->integer", 0, NULL),