diff --git a/lib/chibi/weak.c b/lib/chibi/weak.c
index 7b5701f3..f520fd92 100644
--- a/lib/chibi/weak.c
+++ b/lib/chibi/weak.c
@@ -1,19 +1,16 @@
 /*  weak.c -- weak pointers and ephemerons                    */
-/*  Copyright (c) 2010-2011 Alex Shinn.  All rights reserved. */
+/*  Copyright (c) 2010-2013 Alex Shinn.  All rights reserved. */
 /*  BSD-style license: http://synthcode.com/license.txt       */
 
 #include <chibi/eval.h>
 
-static int sexp_ephemeron_id, sexp_weak_vector_id;
-
-#define sexp_ephemeronp(x) sexp_check_tag(x, sexp_ephemeron_id)
 #define sexp_ephemeron_key(x) sexp_slot_ref(x, 0)
 #define sexp_ephemeron_value(x) sexp_slot_ref(x, 1)
 
 #define sexp_weak_vector_p(x) sexp_check_tag(x, sexp_weak_vector_id)
 
 sexp sexp_make_ephemeron (sexp ctx, sexp self, sexp_sint_t n, sexp key, sexp value) {
-  sexp res = sexp_alloc_type(ctx, pair, sexp_ephemeron_id);
+  sexp res = sexp_alloc_type(ctx, pair, sexp_unbox_fixnum(sexp_opcode_return_type(self)));
   if (! sexp_exceptionp(res)) {
     sexp_ephemeron_key(res) = key;
     sexp_ephemeron_value(res) = value;
@@ -22,6 +19,8 @@ sexp sexp_make_ephemeron (sexp ctx, sexp self, sexp_sint_t n, sexp key, sexp val
 }
 
 sexp sexp_ephemeron_brokenp_op (sexp ctx, sexp self, sexp_sint_t n, sexp eph) {
+  if (! (sexp_pointerp(eph) && (sexp_pointer_tag(eph) == sexp_unbox_fixnum(sexp_opcode_arg1_type(self)))))
+    return sexp_type_exception(ctx, self, sexp_unbox_fixnum(sexp_opcode_arg1_type(self)), eph);
   return sexp_make_boolean(sexp_brokenp(eph));
 }
 
@@ -30,7 +29,7 @@ sexp sexp_make_weak_vector (sexp ctx, sexp self, sexp_sint_t n, sexp len) {
   int i, clen = sexp_unbox_fixnum(len);
   sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, len);
   vec = sexp_alloc_tagged(ctx, sexp_sizeof(vector) + clen*sizeof(sexp),
-                          SEXP_VECTOR);
+                          sexp_unbox_fixnum(sexp_opcode_return_type(self)));
   if (sexp_exceptionp(vec)) return vec;
   x = sexp_vector_data(vec);
   for (i=0; i<clen; i++)
@@ -40,25 +39,32 @@ sexp sexp_make_weak_vector (sexp ctx, sexp self, sexp_sint_t n, sexp len) {
 }
 
 sexp sexp_weak_vector_length (sexp ctx, sexp self, sexp_sint_t n, sexp v) {
-  sexp_assert_type(ctx, sexp_weak_vector_p, sexp_weak_vector_id, v);
+  if (! (sexp_pointerp(v) && (sexp_pointer_tag(v) == sexp_unbox_fixnum(sexp_opcode_arg1_type(self)))))
+    return sexp_type_exception(ctx, self, sexp_unbox_fixnum(sexp_opcode_arg1_type(self)), v);
   return sexp_make_fixnum(sexp_vector_length(v));
 }
 
 sexp sexp_weak_vector_ref (sexp ctx, sexp self, sexp_sint_t n, sexp v, sexp k) {
-  sexp_assert_type(ctx, sexp_weak_vector_p, sexp_weak_vector_id, v);
+  if (! (sexp_pointerp(v) && (sexp_pointer_tag(v) == sexp_unbox_fixnum(sexp_opcode_arg1_type(self)))))
+    return sexp_type_exception(ctx, self, sexp_unbox_fixnum(sexp_opcode_arg1_type(self)), v);
   sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, k);
   return sexp_vector_ref(v, k);
 }
 
 sexp sexp_weak_vector_set (sexp ctx, sexp self, sexp_sint_t n, sexp v, sexp k, sexp x) {
-  sexp_assert_type(ctx, sexp_weak_vector_p, sexp_weak_vector_id, v);
+  if (! (sexp_pointerp(v) && (sexp_pointer_tag(v) == sexp_unbox_fixnum(sexp_opcode_arg1_type(self)))))
+    return sexp_type_exception(ctx, self, sexp_unbox_fixnum(sexp_opcode_arg1_type(self)), v);
   sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, k);
   sexp_vector_set(v, k, x);
   return SEXP_VOID;
 }
 
 sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char* version, sexp_abi_identifier_t abi) {
+#if 0
   sexp v;
+  int sexp_weak_vector_id;
+#endif
+  int sexp_ephemeron_id;
   sexp_gc_var3(name, t, op);
   if (!(sexp_version_compatible(ctx, version, sexp_version)
         && sexp_abi_compatible(ctx, abi, SEXP_ABI_IDENTIFIER)))
@@ -79,9 +85,17 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
   sexp_env_define(ctx, env, name=sexp_intern(ctx, "ephemeron-key", -1), op);
   op = sexp_make_getter(ctx, name=sexp_c_string(ctx, "ephemeron-value", -1), t, SEXP_ONE);
   sexp_env_define(ctx, env, name=sexp_intern(ctx, "ephemeron-value", -1), op);
-  sexp_define_foreign(ctx, env, "make-ephemeron", 2, sexp_make_ephemeron);
-  sexp_define_foreign(ctx, env, "ephemeron-broken?", 1, sexp_ephemeron_brokenp_op);
+  op = sexp_define_foreign(ctx, env, "make-ephemeron", 2, sexp_make_ephemeron);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = sexp_make_fixnum(sexp_ephemeron_id);
+  }
+  op = sexp_define_foreign(ctx, env, "ephemeron-broken?", 1, sexp_ephemeron_brokenp_op);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = sexp_make_fixnum(SEXP_OBJECT);
+    sexp_opcode_arg1_type(op) = sexp_make_fixnum(sexp_ephemeron_id);
+  }
 
+#if 0
   name = sexp_c_string(ctx, "Weak-Vector", -1);
   t = sexp_register_simple_type(ctx, name, SEXP_FALSE, SEXP_ZERO);
   v = sexp_type_by_index(ctx, SEXP_VECTOR);
@@ -92,10 +106,29 @@ sexp sexp_init_library (sexp ctx, sexp self, sexp_sint_t n, sexp env, const char
 
   op = sexp_make_type_predicate(ctx, name=sexp_c_string(ctx,"weak-vector?",-1), t);
   sexp_env_define(ctx, env, name=sexp_intern(ctx, "weak-vector?", -1), op);
-  sexp_define_foreign(ctx, env, "make-weak-vector", 1, sexp_make_weak_vector);
-  sexp_define_foreign(ctx, env, "weak-vector-length", 2, sexp_weak_vector_length);
-  sexp_define_foreign(ctx, env, "weak-vector-ref", 2, sexp_weak_vector_ref);
-  sexp_define_foreign(ctx, env, "weak-vector-set!", 3, sexp_weak_vector_set);
+  op = sexp_define_foreign(ctx, env, "make-weak-vector", 1, sexp_make_weak_vector);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = sexp_make_fixnum(sexp_weak_vector_id);
+    sexp_opcode_arg1_type(op) = sexp_make_fixnum(SEXP_FIXNUM);
+  }
+  op = sexp_define_foreign(ctx, env, "weak-vector-length", 2, sexp_weak_vector_length);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = sexp_make_fixnum(SEXP_FIXNUM);
+    sexp_opcode_arg1_type(op) = sexp_make_fixnum(sexp_weak_vector_id);
+  }
+  op = sexp_define_foreign(ctx, env, "weak-vector-ref", 2, sexp_weak_vector_ref);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = sexp_make_fixnum(SEXP_OBJECT);
+    sexp_opcode_arg1_type(op) = sexp_make_fixnum(sexp_weak_vector_id);
+    sexp_opcode_arg2_type(op) = sexp_make_fixnum(SEXP_FIXNUM);
+  }
+  op = sexp_define_foreign(ctx, env, "weak-vector-set!", 3, sexp_weak_vector_set);
+  if (sexp_opcodep(op)) {
+    sexp_opcode_return_type(op) = SEXP_VOID;
+    sexp_opcode_arg1_type(op) = sexp_make_fixnum(sexp_weak_vector_id);
+    sexp_opcode_arg2_type(op) = sexp_make_fixnum(SEXP_FIXNUM);
+  }
+#endif
 
   sexp_gc_release3(ctx);
   return SEXP_VOID;
diff --git a/lib/chibi/weak.sld b/lib/chibi/weak.sld
index f616bcfd..ecac71bb 100644
--- a/lib/chibi/weak.sld
+++ b/lib/chibi/weak.sld
@@ -4,6 +4,7 @@
 (define-library (chibi weak)
   (export make-ephemeron ephemeron? ephemeron-broken?
           ephemeron-key ephemeron-value
-          make-weak-vector weak-vector? weak-vector-length
-          weak-vector-ref weak-vector-set!)
+          ;; make-weak-vector weak-vector? weak-vector-length
+          ;; weak-vector-ref weak-vector-set!
+          )
   (include-shared "weak"))
diff --git a/tests/weak-tests.scm b/tests/weak-tests.scm
new file mode 100644
index 00000000..3d4565d4
--- /dev/null
+++ b/tests/weak-tests.scm
@@ -0,0 +1,45 @@
+
+(import (chibi weak) (chibi ast) (only (chibi test) test-begin test test-end))
+
+(test-begin "weak pointers")
+
+(test "preserved key and value" '("key" "value" #f)
+  (let ((key (string-append "key"))
+        (value (string-append "value")))
+    (let ((eph (make-ephemeron key value)))
+      (gc)
+      (list key (ephemeron-value eph) (ephemeron-broken? eph)))))
+
+(test "unpreserved key and value" '(#f #f #t)
+  (let ((eph (make-ephemeron (string-append "key") (string-append "value"))))
+    (gc)
+    (list (ephemeron-key eph) (ephemeron-value eph) (ephemeron-broken? eph))))
+
+(test "unpreserved key and preserved value" '(#f "value" #t)
+  (let ((value (string-append "value")))
+    (let ((eph (make-ephemeron (string-append "key") value)))
+      (gc)
+      (list (ephemeron-key eph) value (ephemeron-broken? eph)))))
+
+(test "unpreserved value references unpreserved key" '(#f #f #t)
+  (let ((key (string-append "key")))
+    (let ((eph (make-ephemeron key (cons (string-append "value") key))))
+      (gc)
+      (list (ephemeron-key eph) (ephemeron-value eph) (ephemeron-broken? eph)))))
+
+;; disabled - we support weak keys, but not proper ephemerons
+
+'(test "preserved key and unpreserved value" '("key" "value" #f)
+  (let ((key (string-append "key")))
+    (let ((eph (make-ephemeron key (string-append "value"))))
+      (gc)
+      (list key (ephemeron-value eph) (ephemeron-broken? eph)))))
+
+'(test "preserved value references unpreserved key" '(#f #f #t)
+  (let* ((key (string-append "key"))
+         (value (cons (string-append "value") key)))
+    (let ((eph (make-ephemeron key value)))
+      (gc)
+      (list (ephemeron-key eph) value (ephemeron-broken? eph)))))
+
+(test-end)