diff --git a/src/Authenticator/ChangePasswordHandler.php b/src/Authenticator/ChangePasswordHandler.php
index 41942021..5a662c17 100644
--- a/src/Authenticator/ChangePasswordHandler.php
+++ b/src/Authenticator/ChangePasswordHandler.php
@@ -192,7 +192,7 @@ public function verifyMFACheck(HTTPRequest $request): HTTPResponse
             ], 202);
         }
 
-        $request->getSession()->set(self::MFA_VERIFIED_ON_CHANGE_PASSWORD, true);
+        $request->getSession()->set(ChangePasswordHandler::MFA_VERIFIED_ON_CHANGE_PASSWORD, true);
         $store->clear($request);
 
         return $this->jsonResponse([
@@ -211,7 +211,7 @@ public function changepassword()
             $hash
             && $member
             && $member->RegisteredMFAMethods()->exists()
-            && !$session->get(self::MFA_VERIFIED_ON_CHANGE_PASSWORD)
+            && !$session->get(ChangePasswordHandler::MFA_VERIFIED_ON_CHANGE_PASSWORD)
         ) {
             Injector::inst()->create(StoreInterface::class, $member)->save($this->getRequest());
             return $this->mfa();
diff --git a/src/Authenticator/LoginHandler.php b/src/Authenticator/LoginHandler.php
index 7f764d7c..b05486ec 100644
--- a/src/Authenticator/LoginHandler.php
+++ b/src/Authenticator/LoginHandler.php
@@ -521,7 +521,7 @@ public function getMember()
      * @param LoggerInterface $logger
      * @return $this
      */
-    public function setLogger(LoggerInterface $logger): self
+    public function setLogger(LoggerInterface $logger): LoginHandler
     {
         $this->logger = $logger;
         return $this;
diff --git a/src/BackupCode/VerifyHandler.php b/src/BackupCode/VerifyHandler.php
index 6110a614..c338ff6d 100644
--- a/src/BackupCode/VerifyHandler.php
+++ b/src/BackupCode/VerifyHandler.php
@@ -25,7 +25,7 @@ class VerifyHandler implements VerifyHandlerInterface
      */
     protected $notification;
 
-    public function setNotificationService(Notification $notification): self
+    public function setNotificationService(Notification $notification): VerifyHandler
     {
         $this->notification = $notification;
         return $this;
@@ -92,7 +92,10 @@ public function verify(HTTPRequest $request, StoreInterface $store, RegisteredMe
                 $registeredMethod->Member(),
                 'SilverStripe/MFA/Email/Notification_backupcodeused',
                 [
-                    'subject' => _t(self::class . '.MFAREMOVED', 'A recovery code was used to access your account'),
+                    'subject' => _t(
+                        VerifyHandler::class . '.MFAREMOVED',
+                        'A recovery code was used to access your account'
+                    ),
                     'CodesRemaining' => count($candidates ?? []),
                 ]
             );
diff --git a/src/Controller/AdminRegistrationController.php b/src/Controller/AdminRegistrationController.php
index 2a75cc53..e28d71e0 100644
--- a/src/Controller/AdminRegistrationController.php
+++ b/src/Controller/AdminRegistrationController.php
@@ -272,7 +272,7 @@ protected function jsonResponse(array $response, int $code = 200): HTTPResponse
      * @param LoggerInterface|null $logger
      * @return $this
      */
-    public function setLogger(?LoggerInterface $logger): self
+    public function setLogger(?LoggerInterface $logger): AdminRegistrationController
     {
         $this->logger = $logger;
         return $this;
diff --git a/src/Extension/MemberExtension.php b/src/Extension/MemberExtension.php
index bc072337..20c278b7 100644
--- a/src/Extension/MemberExtension.php
+++ b/src/Extension/MemberExtension.php
@@ -121,7 +121,7 @@ public function updateCMSFields(FieldList $fields): FieldList
      */
     public function currentUserCanViewMFAConfig(): bool
     {
-        return (Permission::check(self::MFA_ADMINISTER_REGISTERED_METHODS)
+        return (Permission::check(MemberExtension::MFA_ADMINISTER_REGISTERED_METHODS)
             || $this->currentUserCanEditMFAConfig());
     }
 
@@ -160,7 +160,7 @@ public function providePermissions(): array
         );
 
         return [
-            self::MFA_ADMINISTER_REGISTERED_METHODS => [
+            MemberExtension::MFA_ADMINISTER_REGISTERED_METHODS => [
                 'name' => $label,
                 'category' => $category,
                 'help' => $description,
diff --git a/src/FormField/RegisteredMFAMethodListField.php b/src/FormField/RegisteredMFAMethodListField.php
index a2cacf2d..65dc4d34 100644
--- a/src/FormField/RegisteredMFAMethodListField.php
+++ b/src/FormField/RegisteredMFAMethodListField.php
@@ -30,7 +30,7 @@ public function __construct(string $name, ?string $title, int $value)
 
     public function Field($properties = array())
     {
-        return $this->renderWith(self::class);
+        return $this->renderWith(RegisteredMFAMethodListField::class);
     }
 
     /**
diff --git a/src/Service/Notification.php b/src/Service/Notification.php
index 84da3fb3..80d5a040 100644
--- a/src/Service/Notification.php
+++ b/src/Service/Notification.php
@@ -43,7 +43,7 @@ class Notification
      */
     protected $logger;
 
-    public function setLogger(LoggerInterface $logger): self
+    public function setLogger(LoggerInterface $logger): Notification
     {
         $this->logger = $logger;
         return $this;
diff --git a/src/Service/RegisteredMethodManager.php b/src/Service/RegisteredMethodManager.php
index 71dadf97..db18eb03 100644
--- a/src/Service/RegisteredMethodManager.php
+++ b/src/Service/RegisteredMethodManager.php
@@ -31,7 +31,7 @@ class RegisteredMethodManager
      */
     protected $notification;
 
-    public function setNotificationService(Notification $notification): self
+    public function setNotificationService(Notification $notification): RegisteredMethodManager
     {
         $this->notification = $notification;
         return $this;
@@ -94,7 +94,7 @@ public function registerForMember(Member $member, MethodInterface $method, $data
                 'SilverStripe/MFA/Email/Notification_register',
                 [
                     'subject' => _t(
-                        self::class . '.MFAADDED',
+                        RegisteredMethodManager::class . '.MFAADDED',
                         'A multi-factor authentication method was added to your account'
                     ),
                     'MethodName' => $method->getName(),
@@ -186,7 +186,7 @@ public function deleteFromMember(Member $member, MethodInterface $method): bool
             'SilverStripe/MFA/Email/Notification_removed',
             [
                 'subject' => _t(
-                    self::class . '.MFAREMOVED',
+                    RegisteredMethodManager::class . '.MFAREMOVED',
                     'A multi-factor authentication method was removed from your account'
                 ),
                 'MethodName' => $method->getName(),
diff --git a/tests/php/Authenticator/RegisterHandlerTest.php b/tests/php/Authenticator/RegisterHandlerTest.php
index abcff8f8..42beab13 100644
--- a/tests/php/Authenticator/RegisterHandlerTest.php
+++ b/tests/php/Authenticator/RegisterHandlerTest.php
@@ -44,7 +44,7 @@ protected function setUp(): void
      */
     public function testRegisterRouteIsPrivateWithGETMethod()
     {
-        $response = $this->get(self::URL);
+        $response = $this->get(RegisterHandlerTest::URL);
         $this->assertEquals(403, $response->getStatusCode());
     }
 
@@ -54,7 +54,7 @@ public function testRegisterRouteIsPrivateWithGETMethod()
     public function testRegisterRouteIsPrivateWithPOSTMethod()
     {
         // See https://github.com/silverstripe/silverstripe-framework/pull/8987 for why we have to provide $data.
-        $response = $this->post(self::URL, ['dummy' => 'data']);
+        $response = $this->post(RegisterHandlerTest::URL, ['dummy' => 'data']);
         $this->assertEquals(403, $response->getStatusCode());
     }
 
@@ -83,7 +83,7 @@ public function testStartRegistrationFailsWhenRegisteredMethodExists()
 
         $this->scaffoldPartialLogin($staleMember);
 
-        $response = $this->get(self::URL);
+        $response = $this->get(RegisterHandlerTest::URL);
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertStringContainsString('This member already has an MFA method', $response->getBody());
     }
@@ -95,7 +95,7 @@ public function testStartRegistrationFailsWhenMethodIsAlreadyRegistered()
     {
         $this->logInAs('stale-member');
 
-        $response = $this->get(self::URL);
+        $response = $this->get(RegisterHandlerTest::URL);
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertStringContainsString(
             'That method has already been registered against this Member',
@@ -113,7 +113,7 @@ public function testStartRegistrationSucceeds()
 
         $this->scaffoldPartialLogin($freshMember);
 
-        $response = $this->get(self::URL);
+        $response = $this->get(RegisterHandlerTest::URL);
         $this->assertEquals(200, $response->getStatusCode(), sprintf('Body: %s', $response->getBody()));
     }
 
@@ -126,7 +126,7 @@ public function testStartRegistrationProvidesACSRFToken()
 
         $this->scaffoldPartialLogin($freshMember);
 
-        $response = $this->get(self::URL);
+        $response = $this->get(RegisterHandlerTest::URL);
         $this->assertEquals(200, $response->getStatusCode(), sprintf('Body: %s', $response->getBody()));
         $this->assertSame(SecurityToken::inst()->getValue(), json_decode($response->getBody())->SecurityID);
     }
@@ -141,7 +141,13 @@ public function testFinishRegistrationFailsWhenCalledDirectly()
 
         $this->scaffoldPartialLogin($freshMember);
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertStringContainsString('No registration in progress', $response->getBody());
     }
@@ -154,9 +160,15 @@ public function testFinishRegistrationFailsWhenMethodIsMismatched()
         /** @var Member $freshMember */
         $freshMember = $this->objFromFixture(Member::class, 'fresh-member');
 
-        $this->scaffoldPartialLogin($freshMember, self::class); // Purposefully set to the wrong class
+        $this->scaffoldPartialLogin($freshMember, RegisterHandlerTest::class); // Purposefully set to the wrong class
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertStringContainsString('Method does not match registration in progress', $response->getBody());
     }
@@ -192,7 +204,13 @@ public function testFinishRegistrationFailsWhenMethodCannotBeRegistered()
 
         $this->scaffoldPartialLogin($freshMember, 'mock-method');
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertStringContainsString('No. Bad user', $response->getBody());
     }
@@ -207,7 +225,13 @@ public function testFinishRegistrationSucceeds()
 
         $this->scaffoldPartialLogin($freshMember, 'basic-math');
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertEquals(201, $response->getStatusCode());
 
         // Make sure the registration made it into the database
@@ -225,14 +249,20 @@ public function testFinishRegistrationValidatesCSRF()
 
         $this->scaffoldPartialLogin($freshMember);
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertEquals(403, $response->getStatusCode());
         $this->assertStringContainsString('Your request timed out', $response->getBody());
 
         $this->scaffoldPartialLogin($freshMember, 'basic-math');
 
         $response = $this->post(
-            self::URL,
+            RegisterHandlerTest::URL,
             [SecurityToken::inst()->getName() => SecurityToken::inst()->getValue()],
             null,
             $this->session(),
@@ -251,7 +281,13 @@ public function testEnforcesSudoMode()
         $freshMember = $this->objFromFixture(Member::class, 'fresh-member');
         $this->scaffoldPartialLogin($freshMember, 'basic-math');
 
-        $response = $this->post(self::URL, ['dummy' => 'data'], null, $this->session(), json_encode(['number' => 7]));
+        $response = $this->post(
+            RegisterHandlerTest::URL,
+            ['dummy' => 'data'],
+            null,
+            $this->session(),
+            json_encode(['number' => 7])
+        );
         $this->assertSame(403, $response->getStatusCode());
         $this->assertStringContainsString('You must be logged in or logging in', (string) $response->getBody());
     }