diff --git a/mailpoet/lib/Automation/Engine/Data/WorkflowRunLog.php b/mailpoet/lib/Automation/Engine/Data/WorkflowRunLog.php
index cceb3b7afe..db1b56d739 100644
--- a/mailpoet/lib/Automation/Engine/Data/WorkflowRunLog.php
+++ b/mailpoet/lib/Automation/Engine/Data/WorkflowRunLog.php
@@ -4,8 +4,6 @@ namespace MailPoet\Automation\Engine\Data;
 
 use DateTimeImmutable;
 use InvalidArgumentException;
-use MailPoet\Automation\Engine\Exceptions\InvalidStateException;
-use MailPoet\Automation\Engine\Exceptions\UnexpectedValueException;
 use MailPoet\Automation\Engine\Utils\Json;
 use Throwable;
 
@@ -92,16 +90,8 @@ class WorkflowRunLog {
    * @return void
    */
   public function setData(string $key, $value): void {
-    try {
-      $newData = $this->getData();
-      $newData[$key] = $value;
-      $encoded = Json::encode($newData);
-      $decoded = Json::decode($encoded);
-      if ($decoded !== $newData) {
-        throw new InvalidArgumentException('$value must be serializable');
-      }
-    } catch (InvalidStateException | InvalidArgumentException | UnexpectedValueException $e) {
-      throw new InvalidArgumentException("Invalid data provided for key $key.");
+    if (!$this->isDataStorable($value)) {
+      throw new InvalidArgumentException("Invalid data provided for key '$key'. Only scalar values and arrays of scalar values are allowed.");
     }
     $this->data[$key] = $value;
   }
@@ -157,4 +147,30 @@ class WorkflowRunLog {
 
     return $workflowRunLog;
   }
+
+  /**
+   * @param mixed $data
+   * @return bool
+   */
+  private function isDataStorable($data): bool {
+    if (is_object($data)) {
+      return false;
+    }
+
+    if (is_scalar($data)) {
+      return true;
+    }
+
+    if (!is_array($data)) {
+      return false;
+    }
+
+    foreach ($data as $value) {
+      if (!$this->isDataStorable($value)) {
+        return false;
+      }
+    }
+
+    return true;
+  }
 }
diff --git a/mailpoet/tests/integration/Automation/Engine/Data/WorkflowRunLogTest.php b/mailpoet/tests/integration/Automation/Engine/Data/WorkflowRunLogTest.php
index 8a88bef0aa..98411c2702 100644
--- a/mailpoet/tests/integration/Automation/Engine/Data/WorkflowRunLogTest.php
+++ b/mailpoet/tests/integration/Automation/Engine/Data/WorkflowRunLogTest.php
@@ -1,4 +1,4 @@
-<?php declare(strict_types=1);
+<?php declare(strict_types = 1);
 
 namespace MailPoet\Test\Automation\Engine\Data;
 
@@ -17,6 +17,7 @@ use MailPoet\Util\Security;
 use MailPoet\Validator\Builder;
 use MailPoet\Validator\Schema\ObjectSchema;
 use MailPoet\WP\Functions as WPFunctions;
+use stdClass;
 
 class WorkflowRunLogTest extends \MailPoetTest {
 
@@ -49,7 +50,7 @@ class WorkflowRunLogTest extends \MailPoetTest {
     $this->wp = new WPFunctions();
   }
 
-  public function testItAllowsSettingData(): void {
+  public function testItAllowsSettingSimpleData(): void {
     $log = new WorkflowRunLog(1, 'step-id');
     $this->assertSame([], $log->getData());
     $log->setData('key', 'value');
@@ -58,16 +59,77 @@ class WorkflowRunLogTest extends \MailPoetTest {
     $this->assertSame('value', $data['key']);
   }
 
-  public function testItDoesNotAllowSettingDataThatCannotBeSaved(): void {
+  public function testItAllowsSettingArraysOfScalarValues(): void {
+    $log = new WorkflowRunLog(1, 'step-id');
+    $data = [
+      'string',
+      11.1,
+      10,
+      true,
+      false
+    ];
+    $log->setData('data', $data);
+    $this->workflowRunLogStorage->createWorkflowRunLog($log);
+    $retrieved = $this->workflowRunLogStorage->getLogsForWorkflowRun(1)[0];
+    expect($retrieved->getData()['data'])->equals($data);
+  }
+
+  public function testItAllowsSettingMultidimensionalArraysOfScalarValues(): void {
+    $log = new WorkflowRunLog(1, 'step-id');
+    $data = [
+      'values' => [
+        'string',
+        11.1,
+        10,
+        true,
+        false
+      ]
+    ];
+    $log->setData('data', $data);
+    $this->workflowRunLogStorage->createWorkflowRunLog($log);
+    $retrieved = $this->workflowRunLogStorage->getLogsForWorkflowRun(1)[0];
+    expect($retrieved->getData()['data'])->equals($data);
+  }
+
+  public function testItDoesNotAllowSettingDataThatIncludesClosures(): void {
     $log = new WorkflowRunLog(1, 'step-id');
     $badData = [
-      function() { echo 'closures cannot be serialized'; }
+      function() {
+        echo 'closures cannot be serialized';
+      }
     ];
     $this->expectException(\InvalidArgumentException::class);
     $log->setData('badData', $badData);
     expect($log->getData())->count(0);
   }
 
+  public function testItDoesNotAllowSettingObjectsForData(): void {
+    $log = new WorkflowRunLog(1, 'step-id');
+    $object = new stdClass();
+    $object->key = 'value';
+    $this->expectException(\InvalidArgumentException::class);
+    $log->setData('object', $object);
+    expect($log->getData())->count(0);
+  }
+
+  public function testItDoesNotAllowSettingMultidimensionalArrayThatContainsNonScalarValue(): void {
+    $log = new WorkflowRunLog(1, 'step-id');
+    $data = [
+      'test' => [
+        'multidimensional' => [
+          'array' => [
+            'values' => [
+              new stdClass()
+            ]
+          ]
+        ]
+      ]
+    ];
+    $this->expectException(\InvalidArgumentException::class);
+    $log->setData('data', $data);
+    expect($log->getData())->count(0);
+  }
+
   public function testItGetsExposedViaAction(): void {
     $this->wp->addAction(Hooks::WORKFLOW_RUN_LOG_AFTER_STEP_RUN, function(WorkflowRunLog $log) {
       $log->setData('test', 'value');
@@ -171,7 +233,9 @@ class WorkflowRunLogTest extends \MailPoetTest {
 
   private function getLogsForAction($callback = null) {
     if ($callback === null) {
-      $callback = function() { return true; };
+      $callback = function() {
+        return true;
+      };
     }
     $testAction = $this->getRegisteredTestAction($callback);
     $actionStep = new Step('action-step-id', Step::TYPE_ACTION, $testAction->getKey(), [], []);
@@ -196,7 +260,9 @@ class WorkflowRunLogTest extends \MailPoetTest {
 
   private function getRegisteredTestAction($callback = null) {
     if ($callback === null) {
-      $callback = function() { return true; };
+      $callback = function() {
+        return true;
+      };
     }
     $action = new TestAction();
     $action->setCallback($callback);