diff --git a/mailpoet/lib/Automation/Engine/Control/StepScheduler.php b/mailpoet/lib/Automation/Engine/Control/StepScheduler.php
index 859f3b27fd..f95c9b426d 100644
--- a/mailpoet/lib/Automation/Engine/Control/StepScheduler.php
+++ b/mailpoet/lib/Automation/Engine/Control/StepScheduler.php
@@ -30,13 +30,19 @@ class StepScheduler {
   }
 
   public function scheduleNextStep(StepRunArgs $args, int $timestamp = null): int {
-    $nextSteps = $args->getStep()->getNextSteps();
+    $step = $args->getStep();
+    $nextSteps = $step->getNextSteps();
 
     // complete the automation run if there are no more steps
     if (count($nextSteps) === 0) {
       $this->completeAutomationRun($args);
       return 0;
     }
+
+    if (count($nextSteps) > 1) {
+      throw Exceptions::nextStepNotScheduled($step->getId());
+    }
+
     return $this->scheduleNextStepByIndex($args, 0, $timestamp);
   }
 
diff --git a/mailpoet/lib/Automation/Engine/Exceptions.php b/mailpoet/lib/Automation/Engine/Exceptions.php
index 75dc19b932..9b4c21ed76 100644
--- a/mailpoet/lib/Automation/Engine/Exceptions.php
+++ b/mailpoet/lib/Automation/Engine/Exceptions.php
@@ -28,6 +28,7 @@ class Exceptions {
   private const FIELD_LOAD_FAILED = 'mailpoet_automation_field_load_failed';
   private const FILTER_NOT_FOUND = 'mailpoet_automation_filter_not_found';
   private const NEXT_STEP_NOT_FOUND = 'mailpoet_next_step_not_found';
+  private const NEXT_STEP_NOT_SCHEDULED = 'mailpoet_next_step_not_scheduled';
   private const AUTOMATION_STRUCTURE_MODIFICATION_NOT_SUPPORTED = 'mailpoet_automation_structure_modification_not_supported';
   private const AUTOMATION_STRUCTURE_NOT_VALID = 'mailpoet_automation_structure_not_valid';
   private const AUTOMATION_STEP_MODIFIED_WHEN_UNKNOWN = 'mailpoet_automation_step_modified_when_unknown';
@@ -191,6 +192,13 @@ class Exceptions {
       ->withMessage(sprintf(__("Automation step with ID '%1\$s' doesn't have a next step with index '%2\$d'.", 'mailpoet'), $stepId, $nextStepId));
   }
 
+  public static function nextStepNotScheduled(string $stepId): InvalidStateException {
+    return InvalidStateException::create()
+      ->withErrorCode(self::NEXT_STEP_NOT_SCHEDULED)
+      // translators: %1$d is the ID of the automation step, %2$s is the ID of the next step.
+      ->withMessage(sprintf(__("Automation step with ID '%s' did not schedule a specific next step, even though multiple next steps are possible.", 'mailpoet'), $stepId));
+  }
+
   public static function automationStructureModificationNotSupported(): UnexpectedValueException {
     return UnexpectedValueException::create()
       ->withErrorCode(self::AUTOMATION_STRUCTURE_MODIFICATION_NOT_SUPPORTED)