diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index 6287d654..26325d58 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -81,7 +81,7 @@ code coverage of the fixed bugs and the new features.
 To run the existing PHPUnit tests, run this command:
 
 ```shell
-composer ci:tests:unit
+composer ci:tests
 ```
 
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 64ea04be..18f59dae 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -144,4 +144,4 @@ jobs:
           composer show;
 
       - name: Run Tests
-        run: composer ci:tests:unit
+        run: composer ci:tests
diff --git a/composer.json b/composer.json
index 4af333b4..a5d91d6d 100644
--- a/composer.json
+++ b/composer.json
@@ -43,10 +43,14 @@
         "symfony/css-selector": "^3.4.32 || ^4.3.5 || ^5.0"
     },
     "require-dev": {
+        "masterminds/html5": "^2.7",
         "php-parallel-lint/php-parallel-lint": "^1.2.0",
         "slevomat/coding-standard": "^4.0.0",
         "squizlabs/php_codesniffer": "^3.5.1"
     },
+    "suggest": {
+      "masterminds/html5": "Use instead of PHP's built-in DOMDocument for HTML5 support."
+    },
     "autoload": {
         "psr-4": {
             "Pelago\\Emogrifier\\": "src/"
@@ -73,9 +77,12 @@
         "ci:php:md": "\"./tools/phpmd.phar\" src text config/phpmd.xml",
         "ci:php:psalm": "\"./tools/psalm.phar\" --show-info=false",
         "ci:tests:unit": "\"./tools/phpunit.phar\"",
+        "ci:tests:html5:unit": "EMOGRIFIER_HTML5=true \"./tools/phpunit.phar\"",
         "ci:tests:sof": "\"./tools/phpunit.phar\" --stop-on-failure",
+        "ci:tests:html5:sof": "EMOGRIFIER_HTML5=true \"./tools/phpunit.phar\" --stop-on-failure",
         "ci:tests": [
-            "@ci:tests:unit"
+            "@ci:tests:unit",
+            "@ci:tests:html5:unit"
         ],
         "ci:dynamic": [
             "@ci:tests"
diff --git a/src/HtmlProcessor/AbstractHtmlProcessor.php b/src/HtmlProcessor/AbstractHtmlProcessor.php
index 479e6e34..0c73695e 100644
--- a/src/HtmlProcessor/AbstractHtmlProcessor.php
+++ b/src/HtmlProcessor/AbstractHtmlProcessor.php
@@ -4,6 +4,9 @@
 
 namespace Pelago\Emogrifier\HtmlProcessor;
 
+use DOMNode;
+use Masterminds\HTML5;
+
 /**
  * Base class for HTML processor that e.g., can remove, add or modify nodes or attributes.
  *
@@ -37,6 +40,11 @@ abstract class AbstractHtmlProcessor
      */
     protected $domDocument = null;
 
+    /**
+     * @var HTML5|null
+     */
+    protected $html5 = null;
+
     /**
      * @var \DOMXPath
      */
@@ -55,19 +63,20 @@ private function __construct()
      * Builds a new instance from the given HTML.
      *
      * @param string $unprocessedHtml raw HTML, must be UTF-encoded, must not be empty
+     * @param bool $html5 use masterminds/html5 parser instead of DOMDocument.
      *
      * @return static
      *
      * @throws \InvalidArgumentException if $unprocessedHtml is anything other than a non-empty string
      */
-    public static function fromHtml(string $unprocessedHtml): self
+    public static function fromHtml(string $unprocessedHtml, ?bool $html5 = null): self
     {
         if ($unprocessedHtml === '') {
             throw new \InvalidArgumentException('The provided HTML must not be empty.', 1515763647);
         }
 
         $instance = new static();
-        $instance->setHtml($unprocessedHtml);
+        $instance->setHtml($unprocessedHtml, $html5);
 
         return $instance;
     }
@@ -91,10 +100,14 @@ public static function fromDomDocument(\DOMDocument $document): self
      * Sets the HTML to process.
      *
      * @param string $html the HTML to process, must be UTF-8-encoded
+     * @param bool $html5 use masterminds/html5 parser instead of DOMDocument.
      */
-    private function setHtml(string $html): void
+    private function setHtml(string $html, ?bool $html5): void
     {
-        $this->createUnifiedDomDocument($html);
+        // If html5 is NULL, fallback to the environment flag.
+        $html5 = $html5 ?? $this->isHtml5Env();
+
+        $this->createUnifiedDomDocument($html, $html5);
     }
 
     /**
@@ -136,7 +149,7 @@ private function setDomDocument(\DOMDocument $domDocument): void
      */
     public function render(): string
     {
-        $htmlWithPossibleErroneousClosingTags = $this->getDomDocument()->saveHTML();
+        $htmlWithPossibleErroneousClosingTags = $this->saveHTML();
 
         return $this->removeSelfClosingTagsClosingTags($htmlWithPossibleErroneousClosingTags);
     }
@@ -148,7 +161,7 @@ public function render(): string
      */
     public function renderBodyContent(): string
     {
-        $htmlWithPossibleErroneousClosingTags = $this->getDomDocument()->saveHTML($this->getBodyElement());
+        $htmlWithPossibleErroneousClosingTags = $this->saveHTML($this->getBodyElement());
         $bodyNodeHtml = $this->removeSelfClosingTagsClosingTags($htmlWithPossibleErroneousClosingTags);
 
         return \preg_replace('%</?+body(?:\\s[^>]*+)?+>%', '', $bodyNodeHtml);
@@ -184,13 +197,36 @@ private function getBodyElement(): \DOMElement
      * The DOM document will always have a BODY element and a document type.
      *
      * @param string $html
+     * @param bool $html5
      */
-    private function createUnifiedDomDocument(string $html): void
+    private function createUnifiedDomDocument(string $html, bool $html5): void
     {
-        $this->createRawDomDocument($html);
+        $html = $this->prepareHtmlForDomConversion($html);
+
+        $html5 ? $this->createHtml5Document($html) : $this->createRawDomDocument($html);
+
         $this->ensureExistenceOfBodyElement();
     }
 
+    /**
+     * Creates a HTML5 document parser instance from the given HTML.
+     *
+     * @param string $html
+     *
+     * @throws \RuntimeException
+     */
+    private function createHtml5Document(string $html): void
+    {
+        if (!\class_exists(HTML5::class)) {
+            throw new \RuntimeException('Class ' . HTML5::class . 'not found. Install the masterminds/html5 library.');
+        }
+
+        $this->html5 = new HTML5(['disable_html_ns' => true]);
+        $domDocument = $this->html5->parse($html);
+
+        $this->setDomDocument($domDocument);
+    }
+
     /**
      * Creates a DOMDocument instance from the given HTML and stores it in $this->domDocument.
      *
@@ -202,7 +238,7 @@ private function createRawDomDocument(string $html): void
         $domDocument->strictErrorChecking = false;
         $domDocument->formatOutput = true;
         $libXmlState = \libxml_use_internal_errors(true);
-        $domDocument->loadHTML($this->prepareHtmlForDomConversion($html));
+        $domDocument->loadHTML($html);
         \libxml_clear_errors();
         \libxml_use_internal_errors($libXmlState);
 
@@ -334,4 +370,40 @@ private function ensureExistenceOfBodyElement(): void
         }
         $htmlElement->appendChild($this->getDomDocument()->createElement('body'));
     }
+
+    /**
+     * Dumps the internal document into a string using HTML formatting.
+     *
+     * @param  DOMNode $dom [optional] parameter to output a subset of the document.
+     *
+     * @return string the HTML, or false if an error occurred.
+     */
+    private function saveHTML(DOMNode $dom = null): string
+    {
+        if (isset($this->html5)) {
+            if ($dom === null) {
+                $dom = $this->domDocument;
+            }
+
+            return $this->html5->saveHTML($dom);
+        }
+
+        // Fall back to DOMDocument.
+        return $this->getDomDocument()->saveHTML($dom);
+    }
+
+    /**
+     * Check whether HTML5 environment is enabled.
+     *
+     * @return bool
+     */
+    private function isHtml5Env(): bool
+    {
+        $env = \getenv('EMOGRIFIER_HTML5');
+        if (is_bool($env)) {
+            return $env;
+        }
+
+        return false;
+    }
 }