diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c3d691c..2d401f0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -42,7 +42,7 @@ jobs:
           php-version: ${{ matrix.php }}
           coverage: xdebug
           extensions: zip
-          tools: composer
+          tools: composer, infection
 
       - name: Determine composer cache directory
         id: composer-cache
@@ -57,8 +57,8 @@ jobs:
 
       - name: Install dependencies
         run: |
-          if [[ "${{ matrix.php }}" == "8.1" ]]; then
-            composer require phpstan/phpstan --no-update
+          if [[ "${{ matrix.php }}" == "8.5" ]]; then
+            composer require --dev phpstan/phpstan:^2.1 --no-update
           fi;
 
           if [[ "${{ matrix.composer }}" == "lowest" ]]; then
@@ -77,11 +77,17 @@ jobs:
           php vendor/bin/phpunit -c phpunit.xml --coverage-clover=build/logs/clover.xml
 
       - name: Run phpstan
-        continue-on-error: true
-        if: ${{ matrix.php == '8.1' }}
+        if: ${{ matrix.php == '8.5' }}
         run: |
           php vendor/bin/phpstan analyse
 
+      - name: Run infection
+        if: ${{ matrix.php == '8.5' }}
+        env:
+          XDEBUG_MODE: coverage
+        run: |
+          infection --threads=max --min-msi=0 --min-covered-msi=0 --only-covering-test-cases --no-progress
+
       - name: Upload coverage results to Coveralls
         continue-on-error: true
         env:
diff --git a/infection.json5 b/infection.json5
new file mode 100644
index 0000000..5b91d70
--- /dev/null
+++ b/infection.json5
@@ -0,0 +1,12 @@
+{
+    "$schema": "https://infection.github.io/schema.json",
+    "staticAnalysisTool": "phpstan",
+    "source": {
+        "directories": [
+            "src"
+        ]
+    },
+    "logs": {
+        "summary": "build/logs/infection-summary.log"
+    }
+}
diff --git a/phpstan.neon b/phpstan.neon
index b58c3b4..5d10cdb 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,4 @@
 parameters:
     level: 8
-    checkMissingIterableValueType: false
     paths:
         - %currentWorkingDirectory%/src/
diff --git a/src/voku/helper/HtmlMin.php b/src/voku/helper/HtmlMin.php
index 42b66f8..b93e29a 100644
--- a/src/voku/helper/HtmlMin.php
+++ b/src/voku/helper/HtmlMin.php
@@ -25,17 +25,6 @@ class HtmlMin implements HtmlMinInterface
      */
     private static $regExSpace = "/[[:space:]]{2,}|[\r\n]/u";
 
-    /**
-     * @var string[]
-     *
-     * @psalm-var list<string>
-     */
-    private static $optional_end_tags = [
-        'html',
-        'head',
-        'body',
-    ];
-
     /**
      * @var string[]
      *
@@ -91,7 +80,7 @@ class HtmlMin implements HtmlMinInterface
     ];
 
     /**
-     * @var array
+     * @var array<string, string>
      */
     private static $booleanAttributes = [
         'allowfullscreen' => '',
@@ -138,7 +127,7 @@ class HtmlMin implements HtmlMinInterface
     ];
 
     /**
-     * @var array
+     * @var list<string>
      */
     private static $skipTagsForRemoveWhitespace = [
         'code',
@@ -149,7 +138,7 @@ class HtmlMin implements HtmlMinInterface
     ];
 
     /**
-     * @var array
+     * @var array<int, string>
      */
     private $protectedChildNodes = [];
 
@@ -375,7 +364,7 @@ public function __construct()
      */
     public function attachObserverToTheDomLoop(HtmlMinDomObserverInterface $observer)
     {
-        $this->domLoopObservers[$observer] = $observer;
+        $this->domLoopObservers->offsetSet($observer, $observer);
     }
 
     /**
@@ -1230,7 +1219,7 @@ private function domNodeOpeningTagOptional(\DOMNode $node): bool
             }
 
             return !\in_array(
-                $firstChild->tagName,
+                $firstChild->nodeName,
                 [
                     'meta',
                     'link',
@@ -1586,7 +1575,7 @@ private function minifyJsonString(string $json): string
     }
 
     /**
-     * @return array
+     * @return string[]
      */
     public function getDomainsToRemoveHttpPrefixFromAttributes(): array
     {
@@ -2266,9 +2255,9 @@ private function protectTagHelper(HtmlDomParser $dom, string $selector): HtmlDom
             }
 
             $parentNode = $element->parentNode();
-            if ($parentNode !== null && $parentNode->nodeValue !== null) {
+            if ($parentNode !== null && $parentNode->getNode()->nodeValue !== null) {
                 $this->protectedChildNodes[$this->protected_tags_counter] = $parentNode->innerHtml();
-                $parentNode->nodeValue = '<' . $this->protectedChildNodesHelper . ' data-' . $this->protectedChildNodesHelper . '="' . $this->protected_tags_counter . '"></' . $this->protectedChildNodesHelper . '>';
+                $parentNode->getNode()->nodeValue = '<' . $this->protectedChildNodesHelper . ' data-' . $this->protectedChildNodesHelper . '="' . $this->protected_tags_counter . '"></' . $this->protectedChildNodesHelper . '>';
             }
 
             ++$this->protected_tags_counter;
@@ -2301,7 +2290,7 @@ private function protectTags(HtmlDomParser $dom): HtmlDomParser
                 }
             }
 
-            $innerHtml = $element->innerhtml;
+            $innerHtml = $element->innerHtml();
 
             // On PHP < 8.0 the simplevokubroken-hash mechanism restores content
             // (including surrounding newlines/spaces) AFTER fixHtmlOutput's trim
@@ -2338,7 +2327,8 @@ private function protectTags(HtmlDomParser $dom): HtmlDomParser
             ) {
                 $originalInnerHtml = $innerHtml;
                 try {
-                    $innerHtml = \JShrink\Minifier::minify($innerHtml);
+                    $minifiedInnerHtml = \JShrink\Minifier::minify($innerHtml);
+                    $innerHtml = \is_string($minifiedInnerHtml) ? $minifiedInnerHtml : $originalInnerHtml;
                 } catch (\Exception $e) {
                     $innerHtml = $originalInnerHtml;
                 }
@@ -2411,6 +2401,9 @@ private function removeComments(HtmlDomParser $dom): HtmlDomParser
         foreach ($dom->findMulti('//comment()') as $commentWrapper) {
             $comment = $commentWrapper->getNode();
             $val = $comment->nodeValue;
+            if ($val === null) {
+                continue;
+            }
             if (\strpos($val, '[') === false) {
                 $parentNode = $comment->parentNode;
                 if ($parentNode !== null) {
@@ -2449,6 +2442,9 @@ private function removeCommentsOnlyFromHtmlString(string $html): string
         foreach ($dom->findMulti('//comment()') as $commentWrapper) {
             $comment = $commentWrapper->getNode();
             $commentValue = $comment->nodeValue;
+            if ($commentValue === null) {
+                continue;
+            }
             if (
                 $this->isConditionalComment($commentValue)
                 ||
@@ -2508,7 +2504,7 @@ private function removeWhitespaceAroundTags(SimpleHtmlDomInterface $element)
     /**
      * Callback function for preg_replace_callback use.
      *
-     * @param array $matches PREG matches
+     * @param array<string, string> $matches PREG matches
      *
      * @return string
      */
@@ -2516,7 +2512,7 @@ private function restoreProtectedHtml($matches): string
     {
         \preg_match('/=["\']*(?<id>\d+)/', $matches['attributes'], $matchesInner);
 
-        return $this->protectedChildNodes[$matchesInner['id']] ?? '';
+        return isset($matchesInner['id']) ? ($this->protectedChildNodes[(int) $matchesInner['id']] ?? '') : '';
     }
 
     /**
@@ -2574,6 +2570,10 @@ private function sumUpWhitespace(HtmlDomParser $dom): HtmlDomParser
                 continue;
             }
 
+            if ($text_node->nodeValue === null) {
+                continue;
+            }
+
             $nodeValueTmp = \preg_replace(self::$regExSpace, ' ', $text_node->nodeValue);
             if ($nodeValueTmp !== null) {
                 $text_node->nodeValue = $nodeValueTmp;
@@ -2600,38 +2600,44 @@ public function useKeepBrokenHtml(bool $keepBrokenHtml): self
     }
 
     /**
-     * @param string[] $templateLogicSyntaxInSpecialScriptTags
+     * @param array<int, mixed> $templateLogicSyntaxInSpecialScriptTags
      *
      * @return HtmlMin
      */
     public function overwriteTemplateLogicSyntaxInSpecialScriptTags(array $templateLogicSyntaxInSpecialScriptTags): self
     {
+        $validatedTemplateLogicSyntaxInSpecialScriptTags = [];
         foreach ($templateLogicSyntaxInSpecialScriptTags as $tmp) {
             if (!\is_string($tmp)) {
-                throw new \InvalidArgumentException('setTemplateLogicSyntaxInSpecialScriptTags only allows string[]');
+                throw new \InvalidArgumentException('overwriteTemplateLogicSyntaxInSpecialScriptTags only allows string[]');
             }
+
+            $validatedTemplateLogicSyntaxInSpecialScriptTags[] = $tmp;
         }
 
-        $this->templateLogicSyntaxInSpecialScriptTags = $templateLogicSyntaxInSpecialScriptTags;
+        $this->templateLogicSyntaxInSpecialScriptTags = $validatedTemplateLogicSyntaxInSpecialScriptTags;
 
         return $this;
     }
 
 
     /**
-     * @param string[] $specialScriptTags
+     * @param array<int, mixed> $specialScriptTags
      *
-     * @return HtmlDomParser
+     * @return HtmlMin
      */
     public function overwriteSpecialScriptTags(array $specialScriptTags): self
     {
+        $validatedSpecialScriptTags = [];
         foreach ($specialScriptTags as $tag) {
             if (!\is_string($tag)) {
-                throw new \InvalidArgumentException('SpecialScriptTags only allows string[]');
+                throw new \InvalidArgumentException('overwriteSpecialScriptTags only allows string[]');
             }
+
+            $validatedSpecialScriptTags[] = $tag;
         }
 
-        $this->specialScriptTags = $specialScriptTags;
+        $this->specialScriptTags = $validatedSpecialScriptTags;
 
         return $this;
     }
diff --git a/src/voku/helper/HtmlMinDomObserverOptimizeAttributes.php b/src/voku/helper/HtmlMinDomObserverOptimizeAttributes.php
index edfa2da..e94ff1f 100644
--- a/src/voku/helper/HtmlMinDomObserverOptimizeAttributes.php
+++ b/src/voku/helper/HtmlMinDomObserverOptimizeAttributes.php
@@ -162,7 +162,7 @@ public function domElementAfterMinification(SimpleHtmlDomInterface $element, Htm
      * @param string           $tag
      * @param string           $attrName
      * @param string           $attrValue
-     * @param array            $allAttr
+     * @param array<string, string> $allAttr
      * @param HtmlMinInterface $htmlMin
      *
      * @return bool
diff --git a/src/voku/helper/HtmlMinInterface.php b/src/voku/helper/HtmlMinInterface.php
index 7a0cfe9..56a3833 100644
--- a/src/voku/helper/HtmlMinInterface.php
+++ b/src/voku/helper/HtmlMinInterface.php
@@ -163,7 +163,7 @@ public function isXHTML(): bool;
     public function getLocalDomains(): array;
 
     /**
-     * @return array
+     * @return string[]
      */
     public function getDomainsToRemoveHttpPrefixFromAttributes(): array;
 }
diff --git a/tests/HtmlMinTest.php b/tests/HtmlMinTest.php
index bb69e2b..adb58d2 100644
--- a/tests/HtmlMinTest.php
+++ b/tests/HtmlMinTest.php
@@ -21,6 +21,63 @@ public function testEmptyResult()
         static::assertSame('', (new HtmlMin())->minify(''));
     }
 
+    public function testAttachObserverToTheDomLoopDoesNotTriggerDeprecation()
+    {
+        $observer = new class implements \voku\helper\HtmlMinDomObserverInterface {
+            /** @var int */
+            public $beforeCalls = 0;
+
+            /** @var int */
+            public $afterCalls = 0;
+
+            public function domElementBeforeMinification(\voku\helper\SimpleHtmlDomInterface $element, \voku\helper\HtmlMinInterface $htmlMin)
+            {
+                ++$this->beforeCalls;
+            }
+
+            public function domElementAfterMinification(\voku\helper\SimpleHtmlDomInterface $element, \voku\helper\HtmlMinInterface $htmlMin)
+            {
+                ++$this->afterCalls;
+            }
+        };
+
+        \set_error_handler(static function (int $severity, string $message, string $file, int $line): bool {
+            if (($severity & \E_DEPRECATED) !== 0) {
+                throw new \ErrorException($message, 0, $severity, $file, $line);
+            }
+
+            return false;
+        });
+
+        try {
+            $minifier = new HtmlMin();
+            $minifier->attachObserverToTheDomLoop($observer);
+
+            static::assertSame('<div class="a b">test</div>', $minifier->minify('<div class="b a">test</div>'));
+        } finally {
+            \restore_error_handler();
+        }
+
+        static::assertGreaterThan(0, $observer->beforeCalls);
+        static::assertGreaterThan(0, $observer->afterCalls);
+    }
+
+    public function testOverwriteTemplateLogicSyntaxInSpecialScriptTagsRejectsNonStringValues()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('overwriteTemplateLogicSyntaxInSpecialScriptTags only allows string[]');
+
+        (new HtmlMin())->overwriteTemplateLogicSyntaxInSpecialScriptTags(['{%', 123]);
+    }
+
+    public function testOverwriteSpecialScriptTagsRejectsNonStringValues()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('overwriteSpecialScriptTags only allows string[]');
+
+        (new HtmlMin())->overwriteSpecialScriptTags(['text/html', 123]);
+    }
+
     /**
      * @return array
      */