diff --git a/src/lib/libatomic.js b/src/lib/libatomic.js
index 0ba48838b7949..dc4fd5cb1b6e5 100644
--- a/src/lib/libatomic.js
+++ b/src/lib/libatomic.js
@@ -7,6 +7,68 @@
 assert(SHARED_MEMORY);
 
 addToLibrary({
+// Chrome 87 shipped Atomics.waitAsync:
+//   https://www.chromestatus.com/feature/6243382101803008
+// However its implementation is faulty:
+//   https://bugs.chromium.org/p/chromium/issues/detail?id=1167541
+// Firefox Nightly 86.0a1 (2021-01-15) does not yet have it:
+//   https://bugzilla.mozilla.org/show_bug.cgi?id=1467846
+// And at the time of writing, no other browser has it either.
+#if MIN_CHROME_VERSION < 91 || MIN_SAFARI_VERSION != TARGET_NOT_SUPPORTED || MIN_FIREFOX_VERSION != TARGET_NOT_SUPPORTED || ENVIRONMENT_MAY_BE_NODE
+  // Partially polyfill Atomics.waitAsync() if not available in the browser.
+  // Also polyfill for old Chrome-based browsers, where Atomics.waitAsync is
+  // broken until Chrome 91, see:
+  //   https://bugs.chromium.org/p/chromium/issues/detail?id=1167541
+  //   https://github.com/tc39/proposal-atomics-wait-async/blob/master/PROPOSAL.md
+  // This polyfill performs polling with setTimeout() to observe a change in the
+  // target memory location.
+  $polyfillWaitAsync__postset: `if (!Atomics.waitAsync || (globalThis.navigator?.userAgent && Number((navigator.userAgent.match(/Chrom(e|ium)\\/([0-9]+)\\./)||[])[2]) < 91)) {
+  let __Atomics_waitAsyncAddresses = [/*[i32a, index, value, maxWaitMilliseconds, promiseResolve]*/];
+  function __Atomics_pollWaitAsyncAddresses() {
+    let now = performance.now();
+    let l = __Atomics_waitAsyncAddresses.length;
+    for (let i = 0; i < l; ++i) {
+      let a = __Atomics_waitAsyncAddresses[i];
+      let expired = (now > a[3]);
+      let awoken = (Atomics.load(a[0], a[1]) != a[2]);
+      if (expired || awoken) {
+        __Atomics_waitAsyncAddresses[i--] = __Atomics_waitAsyncAddresses[--l];
+        __Atomics_waitAsyncAddresses.length = l;
+        a[4](awoken ? 'ok': 'timed-out');
+      }
+    }
+    if (l) {
+      // If we still have addresses to wait, loop the timeout handler to continue polling.
+      setTimeout(__Atomics_pollWaitAsyncAddresses, 10);
+    }
+  }
+  #if ASSERTIONS && WASM_WORKERS
+    if (!ENVIRONMENT_IS_WASM_WORKER) err('Current environment does not support Atomics.waitAsync(): polyfilling it, but this is going to be suboptimal.');
+  #endif
+  /**
+   * @param {number=} maxWaitMilliseconds
+   */
+  Atomics.waitAsync = (i32a, index, value, maxWaitMilliseconds) => {
+    let val = Atomics.load(i32a, index);
+    if (val != value) return { async: false, value: 'not-equal' };
+    if (maxWaitMilliseconds <= 0) return { async: false, value: 'timed-out' };
+    maxWaitMilliseconds = performance.now() + (maxWaitMilliseconds || Infinity);
+    let promiseResolve;
+    let promise = new Promise((resolve) => { promiseResolve = resolve; });
+    if (!__Atomics_waitAsyncAddresses[0]) setTimeout(__Atomics_pollWaitAsyncAddresses, 10);
+    __Atomics_waitAsyncAddresses.push([i32a, index, value, maxWaitMilliseconds, promiseResolve]);
+    return { async: true, value: promise };
+  };
+}`,
+#endif
+
+  $polyfillWaitAsync__internal: true,
+  $polyfillWaitAsync: () => {
+    // nop, used for its postset to ensure `Atomics.waitAsync()` polyfill is
+    // included exactly once and only included when needed.
+    // Any function using Atomics.waitAsync should depend on this.
+  },
+
   $atomicWaitStates__internal: true,
   $atomicWaitStates: ['ok', 'not-equal', 'timed-out'],
   $liveAtomicWaitAsyncs: {},
@@ -14,7 +76,7 @@ addToLibrary({
   $liveAtomicWaitAsyncCounter: 0,
   $liveAtomicWaitAsyncCounter__internal: true,
 
-  emscripten_atomic_wait_async__deps: ['$atomicWaitStates', '$liveAtomicWaitAsyncs', '$liveAtomicWaitAsyncCounter', '$callUserCallback'],
+  emscripten_atomic_wait_async__deps: ['$atomicWaitStates', '$liveAtomicWaitAsyncs', '$liveAtomicWaitAsyncCounter', '$polyfillWaitAsync', '$callUserCallback'],
   emscripten_atomic_wait_async: (addr, val, asyncWaitFinished, userData, maxWaitMilliseconds) => {
     let wait = Atomics.waitAsync(HEAP32, {{{ getHeapOffset('addr', 'i32') }}}, val, maxWaitMilliseconds);
     if (!wait.async) return atomicWaitStates.indexOf(wait.value);
diff --git a/src/lib/libwasm_worker.js b/src/lib/libwasm_worker.js
index 14dd9d0add3d8..8e9162ecd3aca 100644
--- a/src/lib/libwasm_worker.js
+++ b/src/lib/libwasm_worker.js
@@ -298,6 +298,7 @@ if (ENVIRONMENT_IS_WASM_WORKER
     return Atomics.isLockFree(width);
   },
 
+  emscripten_lock_async_acquire__deps: ['$polyfillWaitAsync'],
   emscripten_lock_async_acquire: (lock, asyncWaitFinished, userData, maxWaitMilliseconds) => {
     let dispatch = (val, ret) => {
       setTimeout(() => {