diff --git a/mailpoet/lib/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRule.php b/mailpoet/lib/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRule.php
index ad8d82252a..54d8db0be9 100644
--- a/mailpoet/lib/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRule.php
+++ b/mailpoet/lib/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRule.php
@@ -11,7 +11,10 @@ class ConsistentStepMapRule implements WorkflowNodeVisitor {
   public function initialize(Workflow $workflow): void {
     foreach ($workflow->getSteps() as $id => $step) {
       if ($id !== $step->getId()) {
-        throw Exceptions::workflowStructureNotValid(__('TODO', 'mailpoet'));
+        // translators: %1$s is the ID of the step, %2$s is its index in the steps object.
+        throw Exceptions::workflowStructureNotValid(
+          sprintf(__("Step with ID '%1\$s' stored under a mismatched index '%2\$s'.", 'mailpoet'), $step->getId(), $id)
+        );
       }
     }
   }
diff --git a/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRuleTest.php b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRuleTest.php
index d760719627..cc156fd7f4 100644
--- a/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRuleTest.php
+++ b/mailpoet/tests/unit/Automation/Engine/Validation/WorkflowRules/ConsistentStepMapRuleTest.php
@@ -15,7 +15,7 @@ class ConsistentStepMapRuleTest extends WorkflowRuleTest {
     ]]);
 
     $this->expectException(UnexpectedValueException::class);
-    $this->expectExceptionMessage('Invalid workflow structure: TODO');
+    $this->expectExceptionMessage("Invalid workflow structure: Step with ID 'a' stored under a mismatched index 'root'.");
     (new WorkflowWalker())->walk($workflow, [new ConsistentStepMapRule()]);
   }