diff --git a/src/LimeSurvey/Result/Item/Participant.php b/src/LimeSurvey/Result/Item/Participant.php
index cf89f4b..19590fc 100644
--- a/src/LimeSurvey/Result/Item/Participant.php
+++ b/src/LimeSurvey/Result/Item/Participant.php
@@ -201,7 +201,12 @@ class Participant extends BaseItem
                 break;
 
             case 'completed':
-                $this->completed = 'Y' === trim(strtoupper($value));
+                if ('N' === trim(strtoupper($value))) {
+                    $this->completed = false;
+                    break;
+                }
+
+                $this->completed = Date::isValidDate($value, true);
                 break;
 
             case 'usesleft':
diff --git a/tests/Result/Item/ParticipantTest.php b/tests/Result/Item/ParticipantTest.php
index f7b6d20..3ce6993 100644
--- a/tests/Result/Item/ParticipantTest.php
+++ b/tests/Result/Item/ParticipantTest.php
@@ -200,7 +200,7 @@ class ParticipantTest extends BaseTestCase
                 'sent'           => 'Y',
                 'remindersent'   => 'N',
                 'remindercount'  => 1,
-                'completed'      => 'Y',
+                'completed'      => (new DateTime())->format('Y-m-d H:i'),
                 'usesleft'       => 5,
                 'validfrom'      => (new DateTime())->format('Y-m-d H:i:s'),
                 'validuntil'     => null,