diff --git a/mailpoet/tasks/phpstan/custom-stubs.php b/mailpoet/tasks/phpstan/custom-stubs.php
index 4bbaf09861..01b1a035dd 100644
--- a/mailpoet/tasks/phpstan/custom-stubs.php
+++ b/mailpoet/tasks/phpstan/custom-stubs.php
@@ -66,6 +66,19 @@ namespace {
 
   if (!class_exists(\WP_HTML_Tag_Processor::class)) {
     class WP_HTML_Tag_Processor {
+
+      /** @var int */
+      const MAX_BOOKMARKS = 10;
+
+      /** @var string */
+      protected $html;
+
+      /** @var WP_HTML_Span[] */
+      protected $bookmarks = array();
+
+      /** @var WP_HTML_Text_Replacement[]  */
+      protected $lexical_updates = array();
+
       public function __construct($content) {
       }
 
@@ -80,6 +93,36 @@ namespace {
 
       public function set_attribute($attribute, $value) {
       }
+
+      public function next_token() {}
+
+      public function get_modifiable_text() {}
+
+      public function get_token_type() {}
+
+      public function remove_attribute($name) {}
+
+      public function get_tag() {}
+
+      public function set_modifiable_text($plaintext_content ) {}
+
+      public function set_bookmark($name) {}
+    }
+  }
+
+  if (!class_exists(\WP_HTML_Span::class)) {
+    class WP_HTML_Span {
+      /** @var int */
+      public $start;
+
+      /** @var int */
+      public $length;
+
+      /**
+       * @param int $start  Byte offset into document where replacement span begins.
+       * @param int $length Byte length of span.
+       */
+      public function __construct( int $start, int $length ) {}
     }
   }
 
diff --git a/mailpoet/tasks/phpstan/email-editor-phpstan.neon b/mailpoet/tasks/phpstan/email-editor-phpstan.neon
index 700bf3e98c..163a4cf2c7 100644
--- a/mailpoet/tasks/phpstan/email-editor-phpstan.neon
+++ b/mailpoet/tasks/phpstan/email-editor-phpstan.neon
@@ -10,6 +10,8 @@ parameters:
       - ../../../packages/php/email-editor/tests/_support
       - ../../../packages/php/email-editor/tests/integration
       - ../../../packages/php/email-editor/tests/unit
+  scanFiles:
+    - custom-stubs.php
   inferPrivatePropertyTypeFromConstructor: true
   checkGenericClassInNonGenericObjectType: false
   parallel:
diff --git a/packages/php/email-editor/src/Engine/class-personalizer.php b/packages/php/email-editor/src/Engine/class-personalizer.php
index aedcbf9d7f..1a0791a523 100644
--- a/packages/php/email-editor/src/Engine/class-personalizer.php
+++ b/packages/php/email-editor/src/Engine/class-personalizer.php
@@ -63,6 +63,7 @@ class Personalizer {
 	 * ));
 	 *
 	 * @param array<string, mixed> $context Associative array containing personalization data.
+	 * @return void
 	 */
 	public function set_context( array $context ) {
 		$this->context = $context;
@@ -102,7 +103,7 @@ class Personalizer {
 	 * Parse a personalization tag to the token and attributes.
 	 *
 	 * @param string $token The token to parse.
-	 * @return array{token: string, attributes: array} The parsed token.
+	 * @return array{token: string, arguments: array} The parsed token.
 	 */
 	private function parse_token( string $token ): array {
 		$result = array(
diff --git a/packages/php/email-editor/tests/integration/Engine/Renderer/ContentRenderer/Content_Renderer_Test.php b/packages/php/email-editor/tests/integration/Engine/Renderer/ContentRenderer/Content_Renderer_Test.php
index 7377033ec7..7f23446c24 100644
--- a/packages/php/email-editor/tests/integration/Engine/Renderer/ContentRenderer/Content_Renderer_Test.php
+++ b/packages/php/email-editor/tests/integration/Engine/Renderer/ContentRenderer/Content_Renderer_Test.php
@@ -134,8 +134,8 @@ class Content_Renderer_Test extends \MailPoetTest {
 	 */
 	private function getStylesValueForTag( $html, $tag ): ?string {
 		$html = new \WP_HTML_Tag_Processor( $html );
-		if ( $html->next_tag( $tag ) ) { // @phpstan-ignore-line
-			return $html->get_attribute( 'style' ); // @phpstan-ignore-line
+		if ( $html->next_tag( $tag ) ) {
+			return $html->get_attribute( 'style' );
 		}
 		return null;
 	}
diff --git a/packages/php/email-editor/tests/integration/Engine/Renderer/Renderer_Test.php b/packages/php/email-editor/tests/integration/Engine/Renderer/Renderer_Test.php
index ff4941a11f..1520cea146 100644
--- a/packages/php/email-editor/tests/integration/Engine/Renderer/Renderer_Test.php
+++ b/packages/php/email-editor/tests/integration/Engine/Renderer/Renderer_Test.php
@@ -211,7 +211,7 @@ class Renderer_Test extends \MailPoetTest {
 	private function getStylesValueForTag( string $html, array $query ): ?string {
 		$html = new \WP_HTML_Tag_Processor( $html );
 		if ( $html->next_tag( $query ) ) {
-			return $html->get_attribute( 'style' ); // @phpstan-ignore-line
+			return $html->get_attribute( 'style' );
 		}
 		return null;
 	}
diff --git a/packages/php/email-editor/tests/unit/Engine/PersonalizationTags/Personalization_Tags_Registry_Test.php b/packages/php/email-editor/tests/unit/Engine/PersonalizationTags/Personalization_Tags_Registry_Test.php
index aa7f4e8efc..53479290f0 100644
--- a/packages/php/email-editor/tests/unit/Engine/PersonalizationTags/Personalization_Tags_Registry_Test.php
+++ b/packages/php/email-editor/tests/unit/Engine/PersonalizationTags/Personalization_Tags_Registry_Test.php
@@ -86,6 +86,7 @@ class PersonalizationTagsRegistryTest extends TestCase {
 		$this->registry->register( new Personalization_Tag( 'tag2', 'tag-2', 'Category 2', $callback2 ) );
 
 		// Retrieve the tag and ensure the first registration is preserved.
+		/** @var Personalization_Tag $tag */ // phpcs:ignore Generic.Commenting.DocComment.MissingShort -- used for phpstan
 		$tag = $this->registry->get_by_token( 'tag-1' );
 		$this->assertSame( 'tag1', $tag->get_name() );
 		$this->assertSame( 'Category 1', $tag->get_category() );
diff --git a/packages/php/email-editor/tests/unit/_bootstrap.php b/packages/php/email-editor/tests/unit/_bootstrap.php
index 810e308a09..b4fd6d814a 100644
--- a/packages/php/email-editor/tests/unit/_bootstrap.php
+++ b/packages/php/email-editor/tests/unit/_bootstrap.php
@@ -41,13 +41,21 @@ if ( ! function_exists( 'add_filter' ) ) {
 	 *
 	 * @param string   $tag Tag to add filter for.
 	 * @param callable $callback Callback to call.
+	 * @param int      $priority Optional. Used to specify the order in which the functions
+	 *                                      associated with a particular filter are executed.
+	 *                                      Lower numbers correspond with earlier execution,
+	 *                                      and functions with the same priority are executed
+	 *                                      in the order in which they were added to the filter. Default 10.
+	 * @param int      $accepted_args Optional. The number of arguments the function accepts. Default 1.
+	 * @return bool Always returns true.
 	 */
-	function add_filter( $tag, $callback ) {
+	function add_filter( $tag, $callback, $priority = 10, $accepted_args = 1 ) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.FoundAfterLastUsed
 		global $wp_filters;
 		if ( ! isset( $wp_filters ) ) {
 			$wp_filters = array();
 		}
 		$wp_filters[ $tag ][] = $callback;
+		return true;
 	}
 }
 
@@ -57,8 +65,10 @@ if ( ! function_exists( 'apply_filters' ) ) {
 	 *
 	 * @param string $tag Tag to apply filters for.
 	 * @param mixed  $value Value to filter.
+	 * @param mixed  ...$args   Optional. Additional parameters to pass to the callback functions.
+	 * @return mixed The filtered value after all hooked functions are applied to it.
 	 */
-	function apply_filters( $tag, $value ) {
+	function apply_filters( $tag, $value, ...$args ) { // phpcs:ignore Generic.CodeAnalysis.UnusedFunctionParameter.FoundAfterLastUsed
 		global $wp_filters;
 		if ( isset( $wp_filters[ $tag ] ) ) {
 			foreach ( $wp_filters[ $tag ] as $callback ) {