diff --git a/lib/Config/MP2Migrator.php b/lib/Config/MP2Migrator.php
index 430d321c5a..f85b98b573 100644
--- a/lib/Config/MP2Migrator.php
+++ b/lib/Config/MP2Migrator.php
@@ -944,7 +944,13 @@ class MP2Migrator {
    */
   private function replaceMP2Shortcodes($text) {
     $text = str_replace('[total_subscribers]', '[mailpoet_subscribers_count]', $text);
-    $text = preg_replace_callback('/\[wysija_subscribers_count list_id="(.*)" \]/', array($this, 'replaceMP2ShortcodesCallback'), $text);
+    $text = preg_replace_callback(
+      '/\[wysija_subscribers_count list_id="(.*)" \]/',
+      function ($matches) {
+        return $this->replaceMP2ShortcodesCallback($matches);
+      },
+      $text
+    );
     return $text;
   }
 
diff --git a/lib/Config/Populator.php b/lib/Config/Populator.php
index 9400a036bb..5e08bf6538 100644
--- a/lib/Config/Populator.php
+++ b/lib/Config/Populator.php
@@ -544,6 +544,10 @@ class Populator {
     $task->save();
   }
 
+  /**
+   * Remove this comment when this private function is actually used
+   * @phpcsSuppress SlevomatCodingStandard.Classes.UnusedPrivateElements
+   */
   private function updateFormsSuccessMessages() {
     if (version_compare($this->settings->get('db_version', '3.23.2'), '3.23.1', '>')) {
       return;
diff --git a/lib/Cron/Daemon.php b/lib/Cron/Daemon.php
index 18a7aff74b..8833bdc1a1 100644
--- a/lib/Cron/Daemon.php
+++ b/lib/Cron/Daemon.php
@@ -9,15 +9,11 @@ if (!defined('ABSPATH')) exit;
 class Daemon {
   public $timer;
 
-  /** @var SettingsController */
-  private $settings_controller;
-
   /** @var WorkersFactory */
   private $workers_factory;
 
-  function __construct(SettingsController $settings_controller, WorkersFactory $workers_factory) {
+  function __construct(WorkersFactory $workers_factory) {
     $this->timer = microtime(true);
-    $this->settings_controller = $settings_controller;
     $this->workers_factory = $workers_factory;
   }
 
diff --git a/lib/Cron/Workers/WooCommerceSync.php b/lib/Cron/Workers/WooCommerceSync.php
index 481d8259cb..2acf1e379f 100644
--- a/lib/Cron/Workers/WooCommerceSync.php
+++ b/lib/Cron/Workers/WooCommerceSync.php
@@ -22,8 +22,6 @@ class WooCommerceSync extends SimpleWorker {
   /** @var WooCommerceHelper */
   private $woocommerce_helper;
 
-  private $taskAlreadyInProgress = false;
-
   function __construct(WooCommerceSegment $woocommerce_segment, WooCommerceHelper $woocommerce_helper, $timer = false) {
     $this->woocommerce_segment = $woocommerce_segment;
     $this->woocommerce_helper = $woocommerce_helper;
diff --git a/lib/DI/ContainerConfigurator.php b/lib/DI/ContainerConfigurator.php
index 69cceab83f..ba24ac799b 100644
--- a/lib/DI/ContainerConfigurator.php
+++ b/lib/DI/ContainerConfigurator.php
@@ -123,6 +123,9 @@ class ContainerConfigurator implements IContainerConfigurator {
     return $container;
   }
 
+  /**
+   * @phpcsSuppress SlevomatCodingStandard.Classes.UnusedPrivateElements
+   */
   private function registerPremiumService(ContainerBuilder $container, $id) {
     $container->register($id)
       ->setPublic(true)
diff --git a/lib/Newsletter/Editor/TitleListTransformer.php b/lib/Newsletter/Editor/TitleListTransformer.php
index fa9f691f5a..ac844a1108 100644
--- a/lib/Newsletter/Editor/TitleListTransformer.php
+++ b/lib/Newsletter/Editor/TitleListTransformer.php
@@ -13,7 +13,9 @@ class TitleListTransformer {
   }
 
   function transform($posts) {
-    $results = array_map(array($this, 'getPostTitle'), $posts);
+    $results = array_map(function($post) {
+      return $this->getPostTitle($post);
+    }, $posts);
 
     return array(
       $this->wrap(array(
diff --git a/lib/Subscribers/NewSubscriberNotificationMailer.php b/lib/Subscribers/NewSubscriberNotificationMailer.php
index 4644964948..1c698d29fe 100644
--- a/lib/Subscribers/NewSubscriberNotificationMailer.php
+++ b/lib/Subscribers/NewSubscriberNotificationMailer.php
@@ -19,18 +19,14 @@ class NewSubscriberNotificationMailer {
   /** @var \MailPoet\Mailer\Mailer|null */
   private $mailer;
 
-  /** @var Functions */
-  private $wordpress_functions;
-
   /** @var SettingsController */
   private $settings;
 
   /**
    * @param \MailPoet\Mailer\Mailer|null $mailer
    * @param Renderer|null $renderer
-   * @param Functions|null $wordpress_functions
    */
-  function __construct($mailer = null, $renderer = null, $wordpress_functions = null) {
+  function __construct($mailer = null, $renderer = null) {
     if ($renderer) {
       $this->renderer = $renderer;
     } else {
@@ -38,11 +34,6 @@ class NewSubscriberNotificationMailer {
       $debugging = WP_DEBUG;
        $this->renderer = new Renderer($caching, $debugging);
     }
-    if ($wordpress_functions) {
-      $this->wordpress_functions = $wordpress_functions;
-    } else {
-      $this->wordpress_functions = new Functions();
-    }
     $this->mailer = $mailer;
     $this->settings = new SettingsController();
   }
diff --git a/lib/Tasks/State.php b/lib/Tasks/State.php
index 8bd34fc081..dda23d43b7 100644
--- a/lib/Tasks/State.php
+++ b/lib/Tasks/State.php
@@ -63,7 +63,9 @@ class State
       $tasks = array_merge($tasks, $query->findMany());
     }
 
-    return array_map([$this, 'buildTaskData'], $tasks);
+    return array_map(function ($task) {
+      return $this->buildTaskData($task);
+    }, $tasks);
   }
 
   /**
diff --git a/tasks/code_sniffer/MailPoet/ruleset.xml b/tasks/code_sniffer/MailPoet/ruleset.xml
index 5fff7227db..4782295ce9 100644
--- a/tasks/code_sniffer/MailPoet/ruleset.xml
+++ b/tasks/code_sniffer/MailPoet/ruleset.xml
@@ -3,6 +3,8 @@
   <config name="installed_paths" value="tasks/code_sniffer/vendor/squizlabs/php_codesniffer,tasks/code_sniffer/vendor/phpcompatibility/php-compatibility,tasks/code_sniffer/vendor/slevomat/coding-standard"/>
   <description>MailPoet specific rule set</description>
 
+  <!-- checks for unused methods, unused or write-only properties in a class and unused private constants -->
+  <rule ref="SlevomatCodingStandard.Classes.UnusedPrivateElements"/>
   <!-- This sniff enforces trailing commas in multi-line arrays -->
   <rule ref="SlevomatCodingStandard.Arrays.TrailingArrayComma"/>
   <!-- Disallows assignments in if, elseif and do-while loop conditions -->
diff --git a/tests/integration/Cron/DaemonHttpRunnerTest.php b/tests/integration/Cron/DaemonHttpRunnerTest.php
index 90c532d30b..f226e2e175 100644
--- a/tests/integration/Cron/DaemonHttpRunnerTest.php
+++ b/tests/integration/Cron/DaemonHttpRunnerTest.php
@@ -75,7 +75,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       ]),
     ]);
 
-    $daemon = new Daemon($this->settings, $workers_factory_mock);
+    $daemon = new Daemon($workers_factory_mock);
     $daemon_http_runner = $this->make(new DaemonHttpRunner($daemon), array(
       'pauseExecution' => null,
       'callSelf' => null
@@ -124,7 +124,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       'token' => 123
     );
     $this->settings->set(CronHelper::DAEMON_SETTING, $data);
-    $daemon->__construct(new Daemon($this->settings, $workers_factory_mock));
+    $daemon->__construct(new Daemon($workers_factory_mock));
     $daemon->run($data);
   }
 
@@ -148,7 +148,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       'token' => 123
     );
     $this->settings->set(CronHelper::DAEMON_SETTING, $data);
-    $daemon->__construct(new Daemon($this->settings, $workers_factory_mock));
+    $daemon->__construct(new Daemon($workers_factory_mock));
     $daemon->run($data);
     $data_after_run = $this->settings->get(CronHelper::DAEMON_SETTING);
     expect($data_after_run['token'])->equals(567);
@@ -179,7 +179,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       'token' => 123
     );
     $this->settings->set(CronHelper::DAEMON_SETTING, $data);
-    $daemon_http_runner->__construct(new Daemon($this->settings, $this->createWorkersFactoryMock()));
+    $daemon_http_runner->__construct(new Daemon($this->createWorkersFactoryMock()));
     $daemon_http_runner->run($data);
     $updated_daemon = $this->settings->get(CronHelper::DAEMON_SETTING);
     expect($updated_daemon['token'])->equals($daemon_http_runner->token);
@@ -199,7 +199,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       ]),
     ]);
 
-    $daemon = new Daemon($this->settings, $workers_factory_mock);
+    $daemon = new Daemon($workers_factory_mock);
     $daemon_http_runner = $this->make(new DaemonHttpRunner($daemon), array(
       'pauseExecution' => null,
       'callSelf' => null
@@ -231,7 +231,7 @@ class DaemonHttpRunnerTest extends \MailPoetTest {
       'token' => 123
     );
     $this->settings->set(CronHelper::DAEMON_SETTING, $data);
-    $daemon->__construct(new Daemon($this->settings, $this->createWorkersFactoryMock()));
+    $daemon->__construct(new Daemon($this->createWorkersFactoryMock()));
     $daemon->run($data);
     expect(ignore_user_abort())->equals(1);
   }
diff --git a/tests/integration/Cron/DaemonTest.php b/tests/integration/Cron/DaemonTest.php
index c52ae00906..cc20d319b3 100644
--- a/tests/integration/Cron/DaemonTest.php
+++ b/tests/integration/Cron/DaemonTest.php
@@ -24,7 +24,7 @@ class DaemonTest extends \MailPoetTest {
       'token' => 123
     );
     $this->settings->set(CronHelper::DAEMON_SETTING, $data);
-    $daemon = new Daemon($this->settings, $this->createWorkersFactoryMock());
+    $daemon = new Daemon($this->createWorkersFactoryMock());
     $daemon->run($data);
   }
 
diff --git a/tests/integration/Settings/UserFlagsControllerTest.php b/tests/integration/Settings/UserFlagsControllerTest.php
index 20c52c8f37..32a078f69a 100644
--- a/tests/integration/Settings/UserFlagsControllerTest.php
+++ b/tests/integration/Settings/UserFlagsControllerTest.php
@@ -14,13 +14,10 @@ class UserFlagsControllerTest extends \MailPoetTest {
   /** @var int */
   private $current_user_id;
 
-  /** @var int */
-  private $other_user_id;
-
   function _before() {
     parent::_before();
     UserFlag::deleteMany();
-    
+
     $current_user_id = 1;
     $other_user_id = 2;
     WPFunctions::set(Stub::make(new WPFunctions, [
diff --git a/tests/integration/Subscription/FormTest.php b/tests/integration/Subscription/FormTest.php
index 2be4c42885..d75ef1ee53 100644
--- a/tests/integration/Subscription/FormTest.php
+++ b/tests/integration/Subscription/FormTest.php
@@ -16,9 +16,6 @@ use MailPoet\Util\Url as UrlHelper;
 
 class FormTest extends \MailPoetTest {
 
-  /** @var Form */
-  private $form_controller;
-
   /** @var SettingsController */
   private $settings;