diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 55bbaa5..3a56708 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,10 +43,10 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - run: cp "$(which composer)" composer.phar && ./composer.phar self-update --2.2 # downgrade Composer for HHVM
-      - name: Run hhvm composer.phar install
+      - name: Run hhvm composer.phar require react/promise:^2 # downgrade Promise for HHVM
         uses: docker://hhvm/hhvm:3.30-lts-latest
         with:
-          args: hhvm composer.phar install
+          args: hhvm composer.phar require react/promise:^2
       - name: Run hhvm vendor/bin/phpunit
         uses: docker://hhvm/hhvm:3.30-lts-latest
         with:
diff --git a/README.md b/README.md
index 818bc57..230e16d 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ Timer\timeout(…);
 
 ### timeout()
 
-The `timeout(PromiseInterface<mixed> $promise, float $time, ?LoopInterface $loop = null): PromiseInterface<mixed>` function can be used to
+The `timeout(PromiseInterface<T> $promise, float $time, ?LoopInterface $loop = null): PromiseInterface<T>` function can be used to
 cancel operations that take *too long*.
 
 You need to pass in an input `$promise` that represents a pending operation
@@ -239,7 +239,7 @@ $timer->cancel();
 
 > Deprecated since v1.8.0, see [`sleep()`](#sleep) instead.
 
-The `reject(float $time, ?LoopInterface $loop = null): PromiseInterface<void>` function can be used to
+The `reject(float $time, ?LoopInterface $loop = null): PromiseInterface<never>` function can be used to
 create a new promise which rejects in `$time` seconds with a `TimeoutException`.
 
 ```php
diff --git a/src/functions.php b/src/functions.php
index 1e80087..066b44c 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -129,10 +129,11 @@
  * For more details on the promise primitives, please refer to the
  * [Promise documentation](https://github.com/reactphp/promise#functions).
  *
- * @param PromiseInterface<mixed> $promise
+ * @template T
+ * @param PromiseInterface<T> $promise
  * @param float $time
  * @param ?LoopInterface $loop
- * @return PromiseInterface<mixed>
+ * @return PromiseInterface<T>
  */
 function timeout(PromiseInterface $promise, $time, LoopInterface $loop = null)
 {
@@ -318,7 +319,7 @@ function resolve($time, LoopInterface $loop = null)
  *
  * @param float         $time
  * @param LoopInterface $loop
- * @return PromiseInterface<void>
+ * @return PromiseInterface<never>
  * @deprecated 1.8.0 See `sleep()` instead
  * @see sleep()
  */