diff --git a/.gitattributes b/.gitattributes
index a69a0df..2248014 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -11,6 +11,7 @@
 /phpcs.xml.dist        export-ignore
 /phpstan.neon.dist     export-ignore
 /phpunit.xml.dist      export-ignore
+/phpunitlte9.xml.dist  export-ignore
 /phpunit-bootstrap.php export-ignore
 /PHPCSDebug/Tests      export-ignore
 /Tests                 export-ignore
diff --git a/.github/workflows/quicktest.yml b/.github/workflows/quicktest.yml
index c1e237f..86b84a9 100644
--- a/.github/workflows/quicktest.yml
+++ b/.github/workflows/quicktest.yml
@@ -96,9 +96,22 @@ jobs:
         if: ${{ matrix.phpcs_version == 'dev-master' }}
         run: composer check-complete
 
+      - name: Grab PHPUnit version
+        id: phpunit_version
+        run: echo "VERSION=$(vendor/bin/phpunit --version | grep --only-matching --max-count=1 --extended-regexp '\b[0-9]+\.[0-9]+')" >> $GITHUB_OUTPUT
+
+      - name: Determine PHPUnit composer script to use
+        id: phpunit_script
+        run: |
+          if [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '10.' ) || startsWith( steps.phpunit_version.outputs.VERSION, '11.' ) }}" == "true" ]; then
+            echo 'SUFFIX=' >> $GITHUB_OUTPUT
+          else
+            echo 'SUFFIX=-lte9' >> $GITHUB_OUTPUT
+          fi
+
       - name: Run the unit tests for the PHPCSDebug sniff
-        run: composer test-sniff
+        run: composer test-sniff${{ steps.phpunit_script.outputs.SUFFIX }}
 
       - name: Run the unit tests for the DevTools
         if: ${{ matrix.phpcs_version == 'dev-master' }}
-        run: composer test-tools
+        run: composer test-tools${{ steps.phpunit_script.outputs.SUFFIX }}
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 83994e2..7d63b64 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -150,9 +150,22 @@ jobs:
         if: matrix.phpcs_version == 'dev-master'
         run: composer check-complete
 
+      - name: Grab PHPUnit version
+        id: phpunit_version
+        run: echo "VERSION=$(vendor/bin/phpunit --version | grep --only-matching --max-count=1 --extended-regexp '\b[0-9]+\.[0-9]+')" >> $GITHUB_OUTPUT
+
+      - name: Determine PHPUnit composer script to use
+        id: phpunit_script
+        run: |
+          if [ "${{ startsWith( steps.phpunit_version.outputs.VERSION, '10.' ) || startsWith( steps.phpunit_version.outputs.VERSION, '11.' ) }}" == "true" ]; then
+            echo 'SUFFIX=' >> $GITHUB_OUTPUT
+          else
+            echo 'SUFFIX=-lte9' >> $GITHUB_OUTPUT
+          fi
+
       - name: Run the unit tests for the PHPCSDebug sniff
-        run: composer test-sniff
+        run: composer test-sniff${{ steps.phpunit_script.outputs.SUFFIX }}
 
       - name: Run the unit tests for the DevTools
         if: ${{ matrix.phpcs_version == 'dev-master' }}
-        run: composer test-tools
+        run: composer test-tools${{ steps.phpunit_script.outputs.SUFFIX }}
diff --git a/.gitignore b/.gitignore
index 1b0eeda..817ab77 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,10 @@
+build/
 deploy/
 vendor/
 composer.lock
 .phpcs.xml
 phpcs.xml
 phpunit.xml
+phpunitlte9.xml
 .phpunit.result.cache
 phpstan.neon
diff --git a/composer.json b/composer.json
index eb097c2..a8afd0e 100644
--- a/composer.json
+++ b/composer.json
@@ -28,12 +28,12 @@
     },
     "require-dev" : {
         "roave/security-advisories" : "dev-master",
-        "phpunit/phpunit" : "^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0",
+        "phpunit/phpunit" : "^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0 || ^10.5.32 || ^11.3.3",
         "php-parallel-lint/php-parallel-lint": "^1.4.0",
         "php-parallel-lint/php-console-highlighter": "^1.0.0",
         "phpcsstandards/phpcsdevcs": "^1.1.6",
         "phpcsstandards/phpcsutils" : "^1.0",
-        "yoast/phpunit-polyfills": "^1.1"
+        "yoast/phpunit-polyfills": "^1.1 || ^2.0 || ^3.0"
     },
     "config": {
         "allow-plugins": {
@@ -73,6 +73,15 @@
         "test-tools": [
             "@php ./vendor/phpunit/phpunit/phpunit --testsuite DevTools"
         ],
+        "test-lte9": [
+            "@php ./vendor/phpunit/phpunit/phpunit -c phpunitlte9.xml.dist"
+        ],
+        "test-sniff-lte9": [
+            "@php ./vendor/phpunit/phpunit/phpunit -c phpunitlte9.xml.dist --testsuite DebugSniff"
+        ],
+        "test-tools-lte9": [
+            "@php ./vendor/phpunit/phpunit/phpunit -c phpunitlte9.xml.dist --testsuite DevTools"
+        ],
         "check-complete": [
             "@php ./bin/phpcs-check-feature-completeness ./PHPCSDebug"
         ]
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 7b0a2a1..7d6b0d9 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,16 +1,25 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/7.5/phpunit.xsd"
-    backupGlobals="true"
-    bootstrap="./phpunit-bootstrap.php"
-    beStrictAboutTestsThatDoNotTestAnything="false"
-    convertErrorsToExceptions="true"
-    convertWarningsToExceptions="true"
-    convertNoticesToExceptions="true"
-    convertDeprecationsToExceptions="true"
-    colors="true"
-    forceCoversAnnotation="true">
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd"
+        backupGlobals="true"
+        bootstrap="./phpunit-bootstrap.php"
+        beStrictAboutTestsThatDoNotTestAnything="false"
+        cacheDirectory="build/phpunit-cache"
+        colors="true"
+        displayDetailsOnTestsThatTriggerErrors="true"
+        displayDetailsOnTestsThatTriggerWarnings="true"
+        displayDetailsOnTestsThatTriggerNotices="true"
+        displayDetailsOnTestsThatTriggerDeprecations="true"
+        displayDetailsOnIncompleteTests="true"
+        displayDetailsOnSkippedTests="true"
+        displayDetailsOnPhpunitDeprecations="false"
+        failOnWarning="true"
+        failOnNotice="true"
+        failOnDeprecation="true"
+        failOnPhpunitDeprecation="false"
+        requireCoverageMetadata="true"
+    >
 
     <testsuites>
         <testsuite name="DebugSniff">
diff --git a/phpunitlte9.xml.dist b/phpunitlte9.xml.dist
new file mode 100644
index 0000000..7b0a2a1
--- /dev/null
+++ b/phpunitlte9.xml.dist
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/7.5/phpunit.xsd"
+    backupGlobals="true"
+    bootstrap="./phpunit-bootstrap.php"
+    beStrictAboutTestsThatDoNotTestAnything="false"
+    convertErrorsToExceptions="true"
+    convertWarningsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertDeprecationsToExceptions="true"
+    colors="true"
+    forceCoversAnnotation="true">
+
+    <testsuites>
+        <testsuite name="DebugSniff">
+            <directory suffix="Test.php">./PHPCSDebug/Tests/</directory>
+        </testsuite>
+        <testsuite name="DevTools">
+            <directory suffix="Test.php">./Tests/DocsXsd/</directory>
+        </testsuite>
+    </testsuites>
+</phpunit>