diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 92055ee..867104f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,6 +14,7 @@ jobs:
           - ubuntu-22.04
           - windows-2022
         php:
+          - 8.3
           - 8.2
           - 8.1
           - 8.0
@@ -27,12 +28,14 @@ jobs:
           - 5.4
           - 5.3
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
           coverage: xdebug
           ini-file: development
+      - run: composer config secure-http false && composer config repo.packagist composer http://packagist.org && composer config preferred-install source
+        if: ${{ matrix.php < 5.5 && matrix.os == 'windows-2022' }} # legacy PHP on Windows is allowed to use insecure downloads until it will be removed again
       - run: composer install
       - run: vendor/bin/phpunit --coverage-text
         if: ${{ matrix.php >= 7.3 }}
@@ -45,7 +48,7 @@ jobs:
     runs-on: ubuntu-22.04
     continue-on-error: true
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - run: cp "$(which composer)" composer.phar && ./composer.phar self-update --2.2 # downgrade Composer for HHVM
       - name: Run hhvm composer.phar install
         uses: docker://hhvm/hhvm:3.30-lts-latest
diff --git a/composer.json b/composer.json
index 5750aff..ad50b25 100644
--- a/composer.json
+++ b/composer.json
@@ -32,7 +32,7 @@
         "react/stream": "^1.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.5 || ^5.7 || ^4.8.35",
+        "phpunit/phpunit": "^9.6 || ^5.7 || ^4.8.36",
         "react/socket": "^1.8",
         "sebastian/environment": "^5.0 || ^3.0 || ^2.0 || ^1.0"
     },
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 7a9577e..ac542e7 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
-<!-- PHPUnit configuration file with new format for PHPUnit 9.5+ -->
+<!-- PHPUnit configuration file with new format for PHPUnit 9.6+ -->
 <phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.5/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.6/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          cacheResult="false"
          colors="true"
@@ -20,7 +20,7 @@
     <php>
         <ini name="error_reporting" value="-1" />
         <!-- Evaluate assertions, requires running with "php -d zend.assertions=1 vendor/bin/phpunit" -->
-        <!-- <ini name="zend.assertions=1" value="1" /> -->
+        <!-- <ini name="zend.assertions" value="1" /> -->
         <ini name="assert.active" value="1" />
         <ini name="assert.exception" value="1" />
         <ini name="assert.bail" value="0" />
diff --git a/phpunit.xml.legacy b/phpunit.xml.legacy
index ac5600a..8916116 100644
--- a/phpunit.xml.legacy
+++ b/phpunit.xml.legacy
@@ -18,7 +18,7 @@
     <php>
         <ini name="error_reporting" value="-1" />
         <!-- Evaluate assertions, requires running with "php -d zend.assertions=1 vendor/bin/phpunit" -->
-        <!-- <ini name="zend.assertions=1" value="1" /> -->
+        <!-- <ini name="zend.assertions" value="1" /> -->
         <ini name="assert.active" value="1" />
         <ini name="assert.exception" value="1" />
         <ini name="assert.bail" value="0" />