diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e7721f8..52ad3f0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,6 +28,7 @@ jobs:
         with:
           php-version: ${{ matrix.php }}
           coverage: xdebug
+          ini-file: development
       - run: composer install
       - run: vendor/bin/phpunit --coverage-text --coverage-clover=clover.xml
         if: ${{ matrix.php >= 7.3 }}
diff --git a/composer.json b/composer.json
index a5f576a..394d7e2 100644
--- a/composer.json
+++ b/composer.json
@@ -17,12 +17,16 @@
         "react/http": "^1.6"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.5 || ^5.7 || ^4.8.35"
+        "phpunit/phpunit": "^9.6 || ^5.7 || ^4.8.35"
     },
     "autoload": {
-        "psr-4": { "Clue\\React\\EventSource\\": "src/" }
+        "psr-4": {
+            "Clue\\React\\EventSource\\": "src/"
+        }
     },
     "autoload-dev": {
-        "psr-4": { "Clue\\Tests\\React\\EventSource\\": "tests/" }
+        "psr-4": {
+            "Clue\\Tests\\React\\EventSource\\": "tests/"
+        }
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index ae90046..17a7ce3 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"
@@ -19,5 +19,10 @@
     </coverage>
     <php>
         <ini name="error_reporting" value="-1" />
+        <!-- Evaluate assertions, requires running with "php -d zend.assertions=1 vendor/bin/phpunit" -->
+        <!-- <ini name="zend.assertions" value="1" /> -->
+        <ini name="assert.active" value="1" />
+        <ini name="assert.exception" value="1" />
+        <ini name="assert.bail" value="0" />
     </php>
 </phpunit>
diff --git a/phpunit.xml.legacy b/phpunit.xml.legacy
index 88c631e..154c7e0 100644
--- a/phpunit.xml.legacy
+++ b/phpunit.xml.legacy
@@ -15,4 +15,12 @@
             <directory>./src/</directory>
         </whitelist>
     </filter>
+    <php>
+        <ini name="error_reporting" value="-1" />
+        <!-- Evaluate assertions, requires running with "php -d zend.assertions=1 vendor/bin/phpunit" -->
+        <!-- <ini name="zend.assertions" value="1" /> -->
+        <ini name="assert.active" value="1" />
+        <ini name="assert.exception" value="1" />
+        <ini name="assert.bail" value="0" />
+    </php>
 </phpunit>