diff --git a/aos/AddDisposableResource.js b/aos/AddDisposableResource.js
index 33919f8..541f326 100644
--- a/aos/AddDisposableResource.js
+++ b/aos/AddDisposableResource.js
@@ -29,7 +29,7 @@ module.exports = function AddDisposableResource(disposeCapability, V, hint) {
 
 	var resource;
 	if (arguments.length < 4) { // step 1
-		if (V == null && hint === 'SYNC_DISPOSE') {
+		if (V == null && hint === 'SYNC-DISPOSE') {
 			return 'UNUSED'; // step 1.a
 		}
 		resource = CreateDisposableResource(V, hint); // step 1.c
diff --git a/aos/DisposeResources.js b/aos/DisposeResources.js
index 1a1cbf8..9a342cb 100644
--- a/aos/DisposeResources.js
+++ b/aos/DisposeResources.js
@@ -11,7 +11,6 @@ var $then = callBound('Promise.prototype.then', true);
 
 var CompletionRecord = require('es-abstract/2025/CompletionRecord');
 var Dispose = require('./Dispose');
-var NormalCompletion = require('es-abstract/2025/NormalCompletion');
 var PromiseResolve = require('es-abstract/2025/PromiseResolve');
 var ThrowCompletion = require('es-abstract/2025/ThrowCompletion');
 
@@ -56,9 +55,8 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 	};
 
 	var getPromise = actualHint === 'ASYNC-DISPOSE' && function getPromise(resource) {
-		return $then(
-			promise,
-			function () {
+		var runDispose = function () {
+			try {
 				var result = Dispose( // step 2.a
 					resource['[[ResourceValue]]'],
 					resource['[[Hint]]'],
@@ -67,9 +65,19 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 				if (!result) {
 					throw new $SyntaxError('Assertion failed: non-`~ASYNC-DISPOSE~` resource returned a promise from Dispose');
 				}
-				return $then(result, NormalCompletion);
-			},
-			rejecter
+				return $then(result, void undefined, rejecter);
+			} catch (e) {
+				rejecter(e);
+			}
+			return void undefined;
+		};
+		return $then(
+			promise,
+			runDispose,
+			function (e) {
+				rejecter(e);
+				return runDispose();
+			}
 		);
 	};
 
@@ -96,5 +104,10 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 	// eslint-disable-next-line no-param-reassign
 	disposeCapability['[[DisposableResourceStack]]'] = null; // step 3
 
-	return actualHint === 'ASYNC-DISPOSE' ? promise : completion; // step 4
+	if (actualHint === 'ASYNC-DISPOSE') { // step 4
+		return $then(promise, function () {
+			return completion;
+		});
+	}
+	return completion;
 };
diff --git a/test/tests.js b/test/tests.js
index a4dce47..e823268 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -13,6 +13,7 @@ var semver = require('semver');
 var gOPD = require('gopd');
 var defineAccessorProperty = require('define-accessor-property');
 var SuppressedError = require('suppressed-error/polyfill')();
+var SLOT = require('internal-slot');
 
 var brokenNodePolyfill = semver.satisfies(process.version, '^18.18 || >= 20.4');
 
@@ -99,6 +100,12 @@ module.exports = {
 			instance.use();
 			instance.use(disposable);
 
+			// AddDisposableResource step 1.a: `use(null)` and `use(undefined)` on a sync stack must return without pushing a resource.
+			if (SLOT.has(instance, '[[DisposeCapability]]')) {
+				var cap = SLOT.get(instance, '[[DisposeCapability]]');
+				st.equal(cap['[[DisposableResourceStack]]'].length, 2, '`use(null)` and `use(undefined)` do not add a resource');
+			}
+
 			forEach(v.nonNullPrimitives, function (nonNullishObject) {
 				st['throws'](
 					function () { instance.use(nonNullishObject); },
@@ -614,7 +621,35 @@ module.exports = {
 					function (e) {
 						st.equal(e, throwSentinel, 'throws `throwSentinel`');
 					}
-				);
+				).then(function () {
+					// https://github.com/es-shims/DisposableStack/issues/9
+					var instance3 = new AsyncDisposableStack();
+					var ran = 0;
+					instance3.defer(function () { ran += 1; });
+					instance3.defer(throwsSentinel);
+
+					return instance3.disposeAsync().then(
+						function () {
+							st.fail('dispose with a throwing later disposable failed to throw');
+						},
+						function (e) {
+							st.equal(e, throwSentinel, 'throws `throwSentinel` when an earlier-pushed defer throws');
+							st.equal(ran, 1, 'later-pushed non-throwing defer still ran');
+						}
+					);
+				}).then(function () {
+					var instance4 = new AsyncDisposableStack();
+					instance4.defer(function () { return Promise.reject(throwSentinel); });
+
+					return instance4.disposeAsync().then(
+						function () {
+							st.fail('dispose with a rejecting disposable failed to throw');
+						},
+						function (e) {
+							st.equal(e, throwSentinel, 'rejecting defer surfaces `throwSentinel`');
+						}
+					);
+				});
 			});
 		});