diff --git i/modules/purge_ui/src/Form/PurgerInvalidateForm.php w/modules/purge_ui/src/Form/PurgerInvalidateForm.php
index e8e15f4..ebc84c4 100644
--- i/modules/purge_ui/src/Form/PurgerInvalidateForm.php
+++ w/modules/purge_ui/src/Form/PurgerInvalidateForm.php
@@ -263,27 +263,27 @@ class PurgerInvalidateForm extends ConfirmFormBase {
             ]);
           }
           if ($invalidation->getState() === InvStatesInterface::SUCCEEDED) {
-            drupal_set_message($this->t('Succesfully cleared @object.', ['@object' => $object]));
+            $this->messenger()->addMessage($this->t('Succesfully cleared @object.', ['@object' => $object]));
           }
           elseif ($invalidation->getState() === InvStatesInterface::PROCESSING) {
-            drupal_set_message($this->t('Requested to clear multistep object of type @object!', ['@object' => $object]), 'warning');
+            $this->messenger()->addWarning($this->t('Requested to clear multistep object of type @object!', ['@object' => $object]));
           }
           else {
-            drupal_set_message($this->t('Failed to clear @object!', ['@object' => $object]), 'error');
+            $this->messenger()->addError($this->t('Failed to clear @object!', ['@object' => $object]));
           }
         }
       }
       catch (DiagnosticsException $e) {
         // Diagnostic exceptions happen when the system cannot purge.
-        drupal_set_message($e->getMessage(), 'error');
+        $this->messenger()->addError($e->getMessage());
       }
       catch (CapacityException $e) {
         // Capacity exceptions happen when too much was purged.
-        drupal_set_message($e->getMessage(), 'error');
+        $this->messenger()->addError($e->getMessage());
       }
       catch (LockException $e) {
         // Lock exceptions happen when another code path still processing.
-        drupal_set_message($e->getMessage(), 'error');
+        $this->messenger()->addError($e->getMessage());
       }
 
       $response->addCommand(new ReloadConfigFormCommand('edit-purgers'));