diff --git a/mailpoet/lib/Automation/Engine/Exceptions.php b/mailpoet/lib/Automation/Engine/Exceptions.php
index 852d60bf57..204412c6f7 100644
--- a/mailpoet/lib/Automation/Engine/Exceptions.php
+++ b/mailpoet/lib/Automation/Engine/Exceptions.php
@@ -2,6 +2,7 @@
 
 namespace MailPoet\Automation\Engine;
 
+use MailPoet\Automation\Engine\Data\Step;
 use MailPoet\Automation\Engine\Exceptions\InvalidStateException;
 use MailPoet\Automation\Engine\Exceptions\NotFoundException;
 use MailPoet\Automation\Engine\Exceptions\UnexpectedValueException;
@@ -24,6 +25,7 @@ class Exceptions {
   private const MULTIPLE_SUBJECTS_FOUND = 'mailpoet_automation_multiple_subjects_found';
   private const WORKFLOW_STRUCTURE_MODIFICATION_NOT_SUPPORTED = 'mailpoet_automation_workflow_structure_modification_not_supported';
   private const WORKFLOW_STRUCTURE_NOT_VALID = 'mailpoet_automation_workflow_structure_not_valid';
+  private const WORKFLOW_STEP_MODIFIED_WHEN_UNKNOWN = 'mailpoet_automation_workflow_step_modified_when_unknon';
 
   public function __construct() {
     throw new InvalidStateException(
@@ -147,4 +149,18 @@ class Exceptions {
       // translators: %s is a detailed information
       ->withMessage(sprintf(__("Invalid workflow structure: %s", 'mailpoet'), $detail));
   }
+
+  public static function workflowStepModifiedWhenUnknown(Step $step): UnexpectedValueException {
+    return UnexpectedValueException::create()
+      ->withErrorCode(self::WORKFLOW_STEP_MODIFIED_WHEN_UNKNOWN)
+      // translators: %1$s is the key of the step, %2$s is the type of the step, %3\$s is its ID.
+      ->withMessage(
+        sprintf(
+          __("Modification of step '%1\$s' of type '%2\$s' with ID '%3\$s' is not supported when the related plugin is not active.", 'mailpoet'),
+          $step->getKey(),
+          $step->getType(),
+          $step->getId()
+        )
+      );
+  }
 }
diff --git a/mailpoet/lib/Automation/Engine/Validation/WorkflowStepsValidator.php b/mailpoet/lib/Automation/Engine/Validation/WorkflowStepsValidator.php
new file mode 100644
index 0000000000..79ed89ec03
--- /dev/null
+++ b/mailpoet/lib/Automation/Engine/Validation/WorkflowStepsValidator.php
@@ -0,0 +1,61 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Validation;
+
+use MailPoet\Automation\Engine\Data\Step;
+use MailPoet\Automation\Engine\Data\Workflow;
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Registry;
+use MailPoet\Automation\Engine\Storage\WorkflowStorage;
+use MailPoet\Validator\Validator;
+
+class WorkflowStepsValidator {
+  /** @var Registry */
+  private $registry;
+
+  /** @var Validator */
+  private $validator;
+
+  /** @var WorkflowStorage */
+  private $workflowStorage;
+
+  /** @var Workflow|null|false */
+  private $cachedExistingWorkflow = false;
+
+  public function __construct(
+    Registry $registry,
+    Validator $validator,
+    WorkflowStorage $workflowStorage
+  ) {
+    $this->validator = $validator;
+    $this->registry = $registry;
+    $this->workflowStorage = $workflowStorage;
+  }
+
+  public function validateSteps(Workflow $workflow): void {
+    foreach ($workflow->getSteps() as $step) {
+      $this->validateStep($workflow, $step);
+    }
+  }
+
+  private function validateStep(Workflow $workflow, Step $step): void {
+    $registryStep = $this->registry->getStep($step->getKey());
+    if ($registryStep) {
+      $this->validator->validate($registryStep->getArgsSchema(), $step->getArgs());
+    } else {
+      // step not registered (e.g. plugin was deactivated) - allow saving it only if it hasn't changed
+      $currentWorkflow = $this->getCurrentWorkflow($workflow->getId());
+      $currentStep = $currentWorkflow ? ($currentWorkflow->getSteps()[$step->getId()] ?? null) : null;
+      if (!$currentStep || $step->toArray() !== $currentStep->toArray()) {
+        throw Exceptions::workflowStepModifiedWhenUnknown($step);
+      }
+    }
+  }
+
+  private function getCurrentWorkflow(int $id): ?Workflow {
+    if ($this->cachedExistingWorkflow === false) {
+      $this->cachedExistingWorkflow = $this->workflowStorage->getWorkflow($id);
+    }
+    return $this->cachedExistingWorkflow;
+  }
+}
diff --git a/mailpoet/lib/Automation/Engine/Validation/WorkflowValidator.php b/mailpoet/lib/Automation/Engine/Validation/WorkflowValidator.php
index fff608f709..d957dc049b 100644
--- a/mailpoet/lib/Automation/Engine/Validation/WorkflowValidator.php
+++ b/mailpoet/lib/Automation/Engine/Validation/WorkflowValidator.php
@@ -13,16 +13,22 @@ use MailPoet\Automation\Engine\Validation\WorkflowRules\NoUnreachableStepsRule;
 use MailPoet\Automation\Engine\Validation\WorkflowRules\TriggersUnderRootRule;
 
 class WorkflowValidator {
+  /** @var WorkflowStepsValidator */
+  private $stepsValidator;
+
   /** @var WorkflowWalker */
   private $workflowWalker;
 
   public function __construct(
+    WorkflowStepsValidator $stepsValidator,
     WorkflowWalker $workflowWalker
   ) {
     $this->workflowWalker = $workflowWalker;
+    $this->stepsValidator = $stepsValidator;
   }
 
   public function validate(Workflow $workflow): void {
+    // validate graph
     $this->workflowWalker->walk($workflow, [
       new NoUnreachableStepsRule(),
       new ConsistentStepMapRule(),
@@ -32,5 +38,8 @@ class WorkflowValidator {
       new NoJoinRule(),
       new NoSplitRule(),
     ]);
+
+    // validate steps
+    $this->stepsValidator->validateSteps($workflow);
   }
 }
diff --git a/mailpoet/lib/DI/ContainerConfigurator.php b/mailpoet/lib/DI/ContainerConfigurator.php
index 0afa036538..326a3af953 100644
--- a/mailpoet/lib/DI/ContainerConfigurator.php
+++ b/mailpoet/lib/DI/ContainerConfigurator.php
@@ -129,6 +129,7 @@ class ContainerConfigurator implements IContainerConfigurator {
     $container->autowire(\MailPoet\Automation\Engine\Storage\WorkflowTemplateStorage::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\Engine\Storage\WorkflowStorage::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\Engine\Validation\WorkflowGraph\WorkflowWalker::class)->setPublic(true);
+    $container->autowire(\MailPoet\Automation\Engine\Validation\WorkflowStepsValidator::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\Engine\Validation\WorkflowValidator::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\Engine\WordPress::class)->setPublic(true);
     // Automation - API endpoints