diff --git a/lib/chibi/ast.c b/lib/chibi/ast.c
index 3b878092..3ead140f 100644
--- a/lib/chibi/ast.c
+++ b/lib/chibi/ast.c
@@ -298,11 +298,15 @@ static sexp sexp_object_size (sexp ctx, sexp self, sexp_sint_t n, sexp x) {
 static sexp sexp_integer_to_immediate (sexp ctx, sexp self, sexp_sint_t n, sexp i, sexp dflt) {
   sexp x = (sexp)sexp_unbox_fixnum(i);
   sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, i);
-  if (sexp_pointerp(x))
+  if (!x || sexp_pointerp(x))
     return dflt;
   return x;
 }
 
+static sexp sexp_object_to_integer (sexp ctx, sexp self, sexp_sint_t n, sexp x) {
+  return sexp_make_integer(ctx, (sexp_uint_t)x);
+}
+
 static sexp sexp_make_lambda_op (sexp ctx, sexp self, sexp_sint_t n, sexp name, sexp params, sexp body, sexp locals) {
   sexp res = sexp_alloc_type(ctx, lambda, SEXP_LAMBDA);
   sexp_lambda_name(res) = name;
@@ -559,6 +563,7 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   sexp_define_type(ctx, "Lam", SEXP_LAMBDA);
   sexp_define_type(ctx, "Cnd", SEXP_CND);
   sexp_define_type(ctx, "Set", SEXP_SET);
+  sexp_define_type(ctx, "Set-Syn", SEXP_SET_SYN);
   sexp_define_type(ctx, "Ref", SEXP_REF);
   sexp_define_type(ctx, "Seq", SEXP_SEQ);
   sexp_define_type(ctx, "Lit", SEXP_LIT);
@@ -654,6 +659,7 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   sexp_define_foreign(ctx, env, "core-code", 1, sexp_core_code_op);
   sexp_define_foreign(ctx, env, "object-size", 1, sexp_object_size);
   sexp_define_foreign_opt(ctx, env, "integer->immediate", 2, sexp_integer_to_immediate, SEXP_FALSE);
+  sexp_define_foreign_opt(ctx, env, "object->integer", 1, sexp_object_to_integer, SEXP_FALSE);
   sexp_define_foreign(ctx, env, "gc", 0, sexp_gc_op);
   sexp_define_foreign(ctx, env, "gc-count", 0, sexp_gc_count_op);
   sexp_define_foreign(ctx, env, "gc-usecs", 0, sexp_gc_usecs_op);
diff --git a/lib/chibi/ast.sld b/lib/chibi/ast.sld
index 76a16f23..5ac0d66e 100644
--- a/lib/chibi/ast.sld
+++ b/lib/chibi/ast.sld
@@ -5,7 +5,7 @@
    Object Input-Port Output-Port Opcode Procedure Bytecode Macro Env
    Number Bignum Flonum Integer Complex Char Boolean
    Symbol String Byte-Vector Vector Pair File-Descriptor
-   Context Lam Cnd Set Ref Seq Lit Sc Exception Core
+   Context Lam Cnd Set Set-Syn Ref Seq Lit Sc Exception Core
    syntactic-closure? lambda? cnd? set? ref? seq? lit? type? core?
    environment? bytecode? exception? macro? context? file-descriptor?
    syntactic-closure-expr syntactic-closure-env syntactic-closure-vars
@@ -34,7 +34,7 @@
    extend-env env-parent env-parent-set! env-lambda env-lambda-set!
    env-define! env-push! env-syntactic? env-syntactic?-set! core-code
    type-name type-cpl type-parent type-slots type-num-slots type-printer
-   object-size integer->immediate gc gc-usecs gc-count
+   object-size object->integer integer->immediate gc gc-usecs gc-count
    atomically thread-list abort
    string-contains string-cursor-copy! errno integer->error-string
    flatten-dot update-free-vars! setenv unsetenv safe-setenv)