diff --git a/compat_config.js b/compat_config.js
index 2e2116817..0e84224c4 100644
--- a/compat_config.js
+++ b/compat_config.js
@@ -22,7 +22,7 @@ export default {
       'plugins': [
         // Cf. https://github.com/rollup/rollup-plugin-babel#helpers
         'external-helpers',
-        ['babel-plugin-transform-builtin-extend', {
+        ['transform-builtin-extend', {
           globals: ['Error']
         }]
       ]
diff --git a/fluent/src/fallback.js b/fluent/src/fallback.js
index 7793739c7..5924490c3 100644
--- a/fluent/src/fallback.js
+++ b/fluent/src/fallback.js
@@ -48,7 +48,6 @@
  * @param {string|Array<string>} ids
  * @returns {MessageContext|Array<MessageContext>}
  */
-
 export function mapContextSync(iterable, ids) {
   if (!Array.isArray(ids)) {
     return getContextForId(iterable, ids);
@@ -71,3 +70,36 @@ function getContextForId(iterable, id) {
 
   return null;
 }
+
+/*
+ * Asynchronously map an identifier or an array of identifiers to the best
+ * `MessageContext` instance(s).
+ *
+ * @param {AsyncIterable} iterable
+ * @param {string|Array<string>} ids
+ * @returns {MessageContext|Array<MessageContext>}
+ */
+export async function mapContextAsync(iterable, ids) {
+  if (!Array.isArray(ids)) {
+    for await (const context of iterable) {
+      if (context.hasMessage(ids)) {
+        return context;
+      }
+    }
+  }
+
+  const foundContexts = new Array(ids.length).fill(null);
+
+  for await (const context of iterable) {
+    // XXX Switch to const [index, id] of id.entries() when we move to Babel 7.
+    // See https://github.com/babel/babel/issues/5880.
+    for (let index = 0; index < ids.length; index++) {
+      const id = ids[index];
+      if (!foundContexts[index] && context.hasMessage(id)) {
+        foundContexts[index] = context;
+      }
+    }
+  }
+
+  return foundContexts;
+}
diff --git a/fluent/src/index.js b/fluent/src/index.js
index 4e61c23dc..0bfbfc68b 100644
--- a/fluent/src/index.js
+++ b/fluent/src/index.js
@@ -17,4 +17,4 @@ export {
 } from './types';
 
 export { default as CachedIterable } from './cached_iterable';
-export { mapContextSync } from './fallback';
+export { mapContextSync, mapContextAsync } from './fallback';
diff --git a/fluent/test/fallback_async_test.js b/fluent/test/fallback_async_test.js
new file mode 100644
index 000000000..16ef0e69b
--- /dev/null
+++ b/fluent/test/fallback_async_test.js
@@ -0,0 +1,87 @@
+import assert from 'assert';
+
+import CachedIterable from '../src/cached_iterable';
+import MessageContext from './message_context_stub';
+import { mapContextAsync } from '../src/index';
+
+suite('Async Fallback — single id', function() {
+  let ctx1, ctx2;
+
+  suiteSetup(function() {
+    ctx1 = new MessageContext();
+    ctx1._setMessages(['bar']);
+    ctx2 = new MessageContext();
+    ctx2._setMessages(['foo', 'bar']);
+  });
+
+  test('eager iterable', async function() {
+    const contexts = new CachedIterable([ctx1, ctx2]);
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+  });
+
+  test('eager iterable works more than once', async function() {
+    const contexts = new CachedIterable([ctx1, ctx2]);
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+  });
+
+  test('lazy iterable', async function() {
+    async function *generateMessages() {
+      yield *[ctx1, ctx2];
+    }
+
+    const contexts = new CachedIterable(generateMessages());
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+  });
+
+  test('lazy iterable works more than once', async function() {
+    async function *generateMessages() {
+      yield *[ctx1, ctx2];
+    }
+
+    const contexts = new CachedIterable(generateMessages());
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+    assert.equal(await mapContextAsync(contexts, 'foo'), ctx2);
+    assert.equal(await mapContextAsync(contexts, 'bar'), ctx1);
+  });
+});
+
+suite('Async Fallback — multiple ids', async function() {
+  let ctx1, ctx2;
+
+  suiteSetup(function() {
+    ctx1 = new MessageContext();
+    ctx1._setMessages(['foo', 'bar']);
+    ctx2 = new MessageContext();
+    ctx2._setMessages(['foo', 'bar', 'baz']);
+  });
+
+  test('existing translations', async function() {
+    const contexts = new CachedIterable([ctx1, ctx2]);
+    assert.deepEqual(
+      await mapContextAsync(contexts, ['foo', 'bar']),
+      [ctx1, ctx1]
+    );
+  });
+
+  test('fallback translations', async function() {
+    const contexts = new CachedIterable([ctx1, ctx2]);
+    assert.deepEqual(
+      await mapContextAsync(contexts, ['foo', 'bar', 'baz']),
+      [ctx1, ctx1, ctx2]
+    );
+  });
+
+  test('missing translations', async function() {
+    const contexts = new CachedIterable([ctx1, ctx2]);
+    assert.deepEqual(
+      await mapContextAsync(contexts, ['foo', 'bar', 'baz', 'qux']),
+      [ctx1, ctx1, ctx2, null]
+    );
+  });
+});
diff --git a/fluent/test/fallback_test.js b/fluent/test/fallback_sync_test.js
similarity index 96%
rename from fluent/test/fallback_test.js
rename to fluent/test/fallback_sync_test.js
index 4e9520364..7438d2e9d 100644
--- a/fluent/test/fallback_test.js
+++ b/fluent/test/fallback_sync_test.js
@@ -4,7 +4,7 @@ import CachedIterable from '../src/cached_iterable';
 import MessageContext from './message_context_stub';
 import { mapContextSync } from '../src/index';
 
-suite('Fallback — single id', function() {
+suite('Sync Fallback — single id', function() {
   let ctx1, ctx2;
 
   suiteSetup(function() {
@@ -51,7 +51,7 @@ suite('Fallback — single id', function() {
   });
 });
 
-suite('Fallback — multiple ids', function() {
+suite('Sync Fallback — multiple ids', function() {
   let ctx1, ctx2;
 
   suiteSetup(function() {