diff --git a/src/weakref.cc b/src/weakref.cc
index 4eea618..32f0790 100644
--- a/src/weakref.cc
+++ b/src/weakref.cc
@@ -34,11 +34,24 @@ Nan::Persistent<ObjectTemplate> proxyClass;
 
 Nan::Callback *globalCallback;
 
+// Field index used to store the container object.
+#define FIELD_INDEX_CONTAINER (0)
+
+// Field index used to store the unique pointer value used to identify objects
+// as instances created by this module).
+#define FIELD_INDEX_IDENT (1)
+
+// Count of internal fields used by instances created by this module.
+#define FIELD_COUNT (2)
+
+// The value stored at `FIELD_INDEX_IDENT`, which is designed to be unique to
+// this module, barring intentional mischief from other native code.
+#define IDENT_VALUE ((void *) &proxyClass)
 
 bool IsDead(Local<Object> proxy) {
-  assert(proxy->InternalFieldCount() == 1);
+  assert(proxy->InternalFieldCount() == FIELD_COUNT);
   proxy_container *cont = reinterpret_cast<proxy_container*>(
-    Nan::GetInternalFieldPointer(proxy, 0)
+    Nan::GetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER)
   );
   return cont == NULL || cont->target.IsEmpty();
 }
@@ -47,7 +60,7 @@ bool IsDead(Local<Object> proxy) {
 Local<Object> Unwrap(Local<Object> proxy) {
   assert(!IsDead(proxy));
   proxy_container *cont = reinterpret_cast<proxy_container*>(
-    Nan::GetInternalFieldPointer(proxy, 0)
+    Nan::GetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER)
   );
   Local<Object> _target = Nan::New<Object>(cont->target);
   return _target;
@@ -55,7 +68,7 @@ Local<Object> Unwrap(Local<Object> proxy) {
 
 Local<Object> GetEmitter(Local<Object> proxy) {
   proxy_container *cont = reinterpret_cast<proxy_container*>(
-    Nan::GetInternalFieldPointer(proxy, 0)
+    Nan::GetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER)
   );
   assert(cont != NULL);
   Local<Object> _emitter = Nan::New<Object>(cont->emitter);
@@ -68,7 +81,6 @@ Local<Object> GetEmitter(Local<Object> proxy) {
   const bool dead = IsDead(info.This());  \
   if (!dead) obj = Unwrap(info.This());   \
 
-
 NAN_PROPERTY_GETTER(WeakNamedPropertyGetter) {
   UNWRAP
   info.GetReturnValue().Set(dead ? Local<Value>() : Nan::Get(obj, property).ToLocalChecked());
@@ -148,7 +160,7 @@ static void TargetCallback(const Nan::WeakCallbackInfo<proxy_container> &info) {
 
   // clean everything up
   Local<Object> proxy = Nan::New<Object>(cont->proxy);
-  Nan::SetInternalFieldPointer(proxy, 0, NULL);
+  Nan::SetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER, NULL);
   cont->proxy.Reset();
   cont->emitter.Reset();
   delete cont;
@@ -169,19 +181,23 @@ NAN_METHOD(Create) {
   cont->proxy.Reset(proxy);
   cont->emitter.Reset(_emitter);
   cont->target.Reset(_target);
-  Nan::SetInternalFieldPointer(proxy, 0, cont);
+  Nan::SetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER, cont);
+  Nan::SetInternalFieldPointer(proxy, FIELD_INDEX_IDENT, IDENT_VALUE);
 
   cont->target.SetWeak(cont, TargetCallback, Nan::WeakCallbackType::kParameter);
 
   info.GetReturnValue().Set(proxy);
 }
 
-/**
- * TODO: Make this better.
- */
-
 bool isWeakRef (Local<Value> val) {
-  return val->IsObject() && val.As<Object>()->InternalFieldCount() == 1;
+  if (!val->IsObject()) {
+    return false;
+  }
+
+  Local<Object> obj = val.As<Object>();
+
+  return obj->InternalFieldCount() == FIELD_COUNT
+    && Nan::GetInternalFieldPointer(obj, FIELD_INDEX_IDENT) == IDENT_VALUE;
 }
 
 /**
@@ -216,7 +232,7 @@ NAN_METHOD(IsNearDeath) {
   WEAKREF_FIRST_ARG
 
   proxy_container *cont = reinterpret_cast<proxy_container*>(
-    Nan::GetInternalFieldPointer(proxy, 0)
+    Nan::GetInternalFieldPointer(proxy, FIELD_INDEX_CONTAINER)
   );
   assert(cont != NULL);
 
@@ -273,7 +289,7 @@ NAN_MODULE_INIT(Initialize) {
                                  WeakIndexedPropertyQuery,
                                  WeakIndexedPropertyDeleter,
                                  WeakPropertyEnumerator);
-  p->SetInternalFieldCount(1);
+  p->SetInternalFieldCount(FIELD_COUNT);
 
   Nan::SetMethod(target, "get", Get);
   Nan::SetMethod(target, "isWeakRef", IsWeakRef);
diff --git a/test/create.js b/test/create.js
index 70b30e2..2889325 100644
--- a/test/create.js
+++ b/test/create.js
@@ -20,4 +20,9 @@ describe('create()', function () {
     })
   })
 
+  it('should acknowledge the weakness of created values', function () {
+    var ref = weak.create([]);
+    assert(weak.isWeakRef(ref));
+  })
+
 })
diff --git a/test/promise.js b/test/promise.js
new file mode 100644
index 0000000..55c1812
--- /dev/null
+++ b/test/promise.js
@@ -0,0 +1,14 @@
+var assert = require('assert');
+var weak = require('../')
+
+describe('promise', function () {
+  if (!global.Promise) {
+    // Version of JS without `Promise`; nothing to do.
+    return;
+  }
+
+  it('should not mistake a promise for a weak reference', function () {
+    var p = new Promise(function () {});
+    assert(!weak.isWeakRef(p));
+  });
+})