diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4f08560..7541cfc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,9 +11,10 @@ jobs:
     strategy:
       matrix:
         os:
-          - ubuntu-22.04
+          - ubuntu-24.04
           - windows-2022
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
@@ -43,10 +44,11 @@ jobs:
 
   PHPStan:
     name: PHPStan (PHP ${{ matrix.php }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
@@ -66,10 +68,11 @@ jobs:
 
   Built-in-webserver:
     name: Built-in webserver (PHP ${{ matrix.php }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
@@ -90,7 +93,7 @@ jobs:
 
   Docker:
     name: Docker (${{ matrix.dockerfile }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         dockerfile:
@@ -100,7 +103,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: shivammathur/setup-php@v2
         with:
-          php-version: 8.3
+          php-version: 8.4
       - run: composer install -d tests/integration/
       - run: docker build -f tests/integration/${{ matrix.dockerfile }} tests/integration/
       - run: docker run -d -p 8080:8080 -v "$PWD/composer.json":/app/composer.json $(docker images -q | head -n1)
@@ -112,7 +115,7 @@ jobs:
 
   nginx-reverse-proxy:
     name: nginx (${{ matrix.config.name }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         config:
@@ -124,7 +127,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: shivammathur/setup-php@v2
         with:
-          php-version: 8.3
+          php-version: 8.4
       - run: composer install -d tests/integration/
       - run: docker build -f tests/integration/Dockerfile-basics tests/integration/
       - run: docker run -d -p 8080:8080 -v "$PWD/composer.json":/app/composer.json $(docker images -q | head -n1)
@@ -139,10 +142,11 @@ jobs:
 
   nginx-fpm:
     name: nginx + PHP-FPM (PHP ${{ matrix.php }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
@@ -166,10 +170,11 @@ jobs:
 
   Apache-webserver:
     name: Apache webserver (PHP ${{ matrix.php }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
@@ -192,10 +197,11 @@ jobs:
 
   PHP-webserver:
     name: PHP webserver (PHP ${{ matrix.php }})
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         php:
+          - 8.4
           - 8.3
           - 8.2
           - 8.1
diff --git a/composer.json b/composer.json
index d444a4d..51e2dbf 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
         "react/socket": "^1.15"
     },
     "require-dev": {
-        "phpstan/phpstan": "1.10.47 || 1.4.10",
+        "phpstan/phpstan": "1.12.11 || 1.4.10",
         "phpunit/phpunit": "^9.6 || ^7.5",
         "psr/container": "^2 || ^1",
         "react/promise-timer": "^1.11"
diff --git a/docs/best-practices/deployment.md b/docs/best-practices/deployment.md
index 62ca3a1..5dc2680 100644
--- a/docs/best-practices/deployment.md
+++ b/docs/best-practices/deployment.md
@@ -229,7 +229,7 @@ If you're not already running an Apache server, you can run your X project with
 Apache in a temporary Docker container like this:
 
 ```bash
-$ docker run -it --rm -p 80:80 -v "$PWD":/srv php:8.3-apache sh -c "rmdir /var/www/html;ln -s /srv/public /var/www/html;ln -s /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled; apache2-foreground"
+$ docker run -it --rm -p 80:80 -v "$PWD":/srv php:8.4-apache sh -c "rmdir /var/www/html;ln -s /srv/public /var/www/html;ln -s /etc/apache2/mods-available/rewrite.load /etc/apache2/mods-enabled; apache2-foreground"
 ```
 
 In order to check your web application responds as expected, you can use your
@@ -313,10 +313,10 @@ limit to match your concurrency workload. On Ubuntu- or Debian-based systems,
 you may change your PHP configuration like this:
 
 ```bash
-$ sudoedit /etc/php/8.3/cli/php.ini
+$ sudoedit /etc/php/8.4/cli/php.ini
 ```
 
-```diff title="/etc/php/8.3/cli/php.ini"
+```diff title="/etc/php/8.4/cli/php.ini"
 - memory_limit = 128M
 + memory_limit = -1
 ```
@@ -552,7 +552,7 @@ be achieved by using a `Dockerfile` with the following contents:
 
     ```docker title="Dockerfile"
     # syntax=docker/dockerfile:1
-    FROM php:8.3-cli
+    FROM php:8.4-cli
 
     WORKDIR /app/
     COPY public/ public/
@@ -574,7 +574,7 @@ be achieved by using a `Dockerfile` with the following contents:
     COPY composer.json composer.lock ./
     RUN composer install --no-dev --ignore-platform-reqs --optimize-autoloader
 
-    FROM php:8.3-alpine
+    FROM php:8.4-alpine
 
     # recommended: install optional extensions ext-ev and ext-sockets
     RUN apk --no-cache add ${PHPIZE_DEPS} libev linux-headers \ 
diff --git a/tests/AppTest.php b/tests/AppTest.php
index a664012..ab7a4ae 100644
--- a/tests/AppTest.php
+++ b/tests/AppTest.php
@@ -1437,9 +1437,11 @@ public function testInvokeWithMatchingRouteReturnsInternalServerErrorResponseWhe
     {
         $app = $this->createAppWithoutLogger();
 
-        $line = __LINE__ + 3;
+        // expect error on next line (should yield PromiseInterface)
+        // return on same line because PHP < 8.4 reports error on statement *after* invalid yield
+        $line = __LINE__ + 2;
         $app->get('/users', function () {
-            yield null;
+            return yield null;
         });
 
         $request = new ServerRequest('GET', 'http://localhost/users');
diff --git a/tests/ContainerTest.php b/tests/ContainerTest.php
index 93829d7..a3f7899 100644
--- a/tests/ContainerTest.php
+++ b/tests/ContainerTest.php
@@ -1284,7 +1284,7 @@ public function __construct(\stdClass $data)
         $callable = $container->callable(get_class($controller));
 
         $this->expectException(\BadMethodCallException::class);
-        $this->expectExceptionMessage('Argument 1 ($username) of {closure}() is not defined');
+        $this->expectExceptionMessageMatches('/Argument 1 \(\$username\) of {closure(:[^{}]+)?}\(\) is not defined$/');
         $callable($request);
     }
 
@@ -1770,7 +1770,7 @@ public function testCallableReturnsCallableThatThrowsWhenFactoryRequiresUntypedA
         $callable = $container->callable(\stdClass::class);
 
         $this->expectException(\BadMethodCallException::class);
-        $this->expectExceptionMessage('Argument 1 ($undefined) of {closure}() has no type');
+        $this->expectExceptionMessageMatches('/Argument 1 \(\$undefined\) of {closure(:[^{}]+)?}\(\) has no type$/');
         $callable($request);
     }
 
@@ -1788,7 +1788,7 @@ public function testCallableReturnsCallableThatThrowsWhenFactoryRequiresUndefine
         $callable = $container->callable(\stdClass::class);
 
         $this->expectException(\BadMethodCallException::class);
-        $this->expectExceptionMessage('Argument 1 ($undefined) of {closure}() is not defined');
+        $this->expectExceptionMessageMatches('/Argument 1 \(\$undefined\) of {closure(:[^{}]+)?}\(\) is not defined$/');
         $callable($request);
     }
 
@@ -1803,7 +1803,7 @@ public function testCallableReturnsCallableThatThrowsWhenFactoryRequiresRecursiv
         $callable = $container->callable(\stdClass::class);
 
         $this->expectException(\BadMethodCallException::class);
-        $this->expectExceptionMessage('Argument 1 ($data) of {closure}() is recursive');
+        $this->expectExceptionMessageMatches('/Argument 1 \(\$data\) of {closure(:[^{}]+)?}\(\) is recursive$/');
         $callable($request);
     }
 
@@ -2233,4 +2233,16 @@ public function testCtorWithInvalidValueThrows(): void
         $this->expectExceptionMessage('Argument #1 ($loader) must be of type array|Psr\Container\ContainerInterface, stdClass given');
         new Container((object) []); // @phpstan-ignore-line
     }
+
+    public function expectExceptionMessageMatches(string $regularExpression): void
+    {
+        if (method_exists(parent::class, 'expectExceptionMessageMatches')) {
+            // @phpstan-ignore-next-line PHPUnit 8.4+
+            parent::expectExceptionMessageMatches($regularExpression);
+        } else {
+            // legacy PHPUnit
+            assert(method_exists($this, 'expectExceptionMessageRegExp'));
+            $this->expectExceptionMessageRegExp($regularExpression);
+        }
+    }
 }
diff --git a/tests/Io/LogStreamHandlerTest.php b/tests/Io/LogStreamHandlerTest.php
index f4a77ad..2e8248a 100644
--- a/tests/Io/LogStreamHandlerTest.php
+++ b/tests/Io/LogStreamHandlerTest.php
@@ -257,6 +257,7 @@ public function testLogWithPathToExistingFileWillAppendLogMessageWithCurrentDate
         assert(is_resource($stream));
         fwrite($stream, 'First' . PHP_EOL);
 
+        /** @var array{uri:string} */
         $meta = stream_get_meta_data($stream);
         assert(is_string($meta['uri']));
 
diff --git a/tests/integration/Dockerfile-basics b/tests/integration/Dockerfile-basics
index 270aa38..b54d9cf 100644
--- a/tests/integration/Dockerfile-basics
+++ b/tests/integration/Dockerfile-basics
@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1
-FROM php:8.3-cli
+FROM php:8.4-cli
 
 WORKDIR /app/
 COPY public/ public/
diff --git a/tests/integration/Dockerfile-production b/tests/integration/Dockerfile-production
index ccf3b48..71211d0 100644
--- a/tests/integration/Dockerfile-production
+++ b/tests/integration/Dockerfile-production
@@ -8,7 +8,7 @@ COPY composer.json composer.lock ./
 # dev environment already has dependencies installed:
 COPY vendor/ vendor/
 
-FROM php:8.3-alpine
+FROM php:8.4-alpine
 
 # recommended: install optional extensions ext-ev and ext-sockets
 RUN apk --no-cache add ${PHPIZE_DEPS} libev linux-headers \