diff --git a/eval.c b/eval.c
index d7e0bc93..017abf6f 100644
--- a/eval.c
+++ b/eval.c
@@ -399,18 +399,6 @@ static sexp sexp_make_macro (sexp ctx, sexp p, sexp e) {
   return mac;
 }
 
-sexp sexp_make_variable_transformer_op (sexp ctx, sexp self, sexp_sint_t n, sexp base_proc) {
-  sexp flags;
-  sexp_assert_type(ctx, sexp_procedurep, SEXP_PROCEDURE, base_proc);
-  if (sexp_procedure_variable_transformer_p(base_proc))
-    return base_proc;
-  flags = sexp_make_fixnum(sexp_unbox_fixnum(sexp_procedure_flags(base_proc)) | SEXP_PROC_VARIABLE_TRANSFORMER);
-  return sexp_make_procedure(ctx, flags,
-                             sexp_make_fixnum(sexp_procedure_num_args(base_proc)),
-                             sexp_procedure_code(base_proc),
-                             sexp_procedure_vars(base_proc));
-}
-
 sexp sexp_make_synclo_op (sexp ctx, sexp self, sexp_sint_t n, sexp env, sexp fv, sexp expr) {
   sexp res;
   sexp_assert_type(ctx, sexp_envp, SEXP_ENV, env);
diff --git a/include/chibi/eval.h b/include/chibi/eval.h
index bbd905cf..ebbad05d 100644
--- a/include/chibi/eval.h
+++ b/include/chibi/eval.h
@@ -128,7 +128,6 @@ SEXP_API sexp sexp_warn_undefs_op (sexp ctx, sexp self, sexp_sint_t n, sexp from
 SEXP_API sexp sexp_make_lit (sexp ctx, sexp value);
 SEXP_API sexp sexp_make_opcode (sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp, sexp_proc1);
 SEXP_API sexp sexp_make_procedure_op (sexp ctx, sexp self, sexp_sint_t n, sexp flags, sexp num_args, sexp bc, sexp vars);
-SEXP_API sexp sexp_make_variable_transformer_op (sexp ctx, sexp self, sexp_sint_t n, sexp base_proc);
 SEXP_API sexp sexp_define_foreign_aux (sexp ctx, sexp env, const char *name, int num_args, int flags, const char *fname, sexp_proc1 f, sexp data);
 SEXP_API sexp sexp_register_optimization(sexp ctx, sexp self, sexp_sint_t n, sexp f, sexp i);
 #if SEXP_USE_AUTO_FORCE
diff --git a/lib/chibi/ast.c b/lib/chibi/ast.c
index ab952197..50b295ca 100644
--- a/lib/chibi/ast.c
+++ b/lib/chibi/ast.c
@@ -108,6 +108,18 @@ sexp sexp_get_procedure_flags (sexp ctx, sexp self, sexp_sint_t n, sexp proc) {
   return sexp_make_fixnum(sexp_procedure_flags(proc));
 }
 
+sexp sexp_make_variable_transformer_op (sexp ctx, sexp self, sexp_sint_t n, sexp base_proc) {
+  sexp flags;
+  sexp_assert_type(ctx, sexp_procedurep, SEXP_PROCEDURE, base_proc);
+  if (sexp_procedure_variable_transformer_p(base_proc))
+    return base_proc;
+  flags = sexp_make_fixnum(sexp_unbox_fixnum(sexp_procedure_flags(base_proc)) | SEXP_PROC_VARIABLE_TRANSFORMER);
+  return sexp_make_procedure(ctx, flags,
+                             sexp_make_fixnum(sexp_procedure_num_args(base_proc)),
+                             sexp_procedure_code(base_proc),
+                             sexp_procedure_vars(base_proc));
+}
+
 sexp sexp_get_opcode_name (sexp ctx, sexp self, sexp_sint_t n, sexp op) {
   if (! sexp_opcodep(op))
     return sexp_type_exception(ctx, self, SEXP_OPCODE, op);
@@ -701,6 +713,7 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   sexp_define_foreign(ctx, env, "procedure-variadic?", 1, sexp_get_procedure_variadic_p);
   sexp_define_foreign(ctx, env, "procedure-variable-transformer?", 1, sexp_get_procedure_variable_transformer_p);
   sexp_define_foreign(ctx, env, "procedure-flags", 1, sexp_get_procedure_flags);
+  sexp_define_foreign(ctx, env, "make-variable-transformer", 1, sexp_make_variable_transformer_op);
   sexp_define_foreign(ctx, env, "copy-lambda", 1, sexp_copy_lambda);
   sexp_define_foreign_opt(ctx, env, "make-lambda", 4, sexp_make_lambda_op, SEXP_NULL);
   sexp_define_foreign_opt(ctx, env, "make-cnd", 3, sexp_make_cnd_op, SEXP_VOID);
diff --git a/lib/chibi/ast.sld b/lib/chibi/ast.sld
index 8cbcd0af..40b99919 100644
--- a/lib/chibi/ast.sld
+++ b/lib/chibi/ast.sld
@@ -29,7 +29,7 @@
    macro-procedure macro-env macro-source macro-aux macro-aux-set!
    procedure-code procedure-vars procedure-name procedure-name-set!
    procedure-arity procedure-variadic? procedure-variable-transformer?
-   procedure-flags make-procedure
+   procedure-flags make-variable-transformer make-procedure
    bytecode-name bytecode-literals bytecode-source
    port-line port-line-set! port-source? port-source?-set!
    extend-env env-parent env-parent-set! env-lambda env-lambda-set!
diff --git a/opcodes.c b/opcodes.c
index fc66db3e..552fc698 100644
--- a/opcodes.c
+++ b/opcodes.c
@@ -197,7 +197,6 @@ _FN2(_I(SEXP_OBJECT), _I(SEXP_OBJECT), SEXP_NULL, "memq", 0, sexp_memq_op),
 _FN2(_I(SEXP_OBJECT), _I(SEXP_OBJECT), SEXP_NULL, "assq", 0, sexp_assq_op),
 _FN3(_I(SEXP_SYNCLO), _I(SEXP_ENV), SEXP_NULL, _I(SEXP_OBJECT), "make-syntactic-closure", 0, sexp_make_synclo_op),
 _FN1(_I(SEXP_OBJECT), _I(SEXP_OBJECT), "strip-syntactic-closures", 0, sexp_strip_synclos),
-_FN1(_I(SEXP_PROCEDURE), _I(SEXP_PROCEDURE), "make-variable-transformer", 0, sexp_make_variable_transformer_op),
 _FN0(_I(SEXP_OPORT), "open-output-string", 0, sexp_open_output_string_op),
 _FN1(_I(SEXP_IPORT), _I(SEXP_STRING), "open-input-string", 0, sexp_open_input_string_op),
 _FN1(_I(SEXP_STRING), _I(SEXP_OPORT), "get-output-string", 0, sexp_get_output_string_op),