diff --git a/lib/Db/Card.php b/lib/Db/Card.php
index e6823b37b..5599aef76 100644
--- a/lib/Db/Card.php
+++ b/lib/Db/Card.php
@@ -125,15 +125,18 @@ class Card extends RelationalEntity {
 		$this->databaseType = $type;
 	}
 
-	public function getDuedate($isoFormat = false) {
-		if ($this->duedate === null) {
-			return null;
-		}
-		$dt = new DateTime($this->duedate);
+	public function getDueDateTime(): ?DateTime {
+		return $this->duedate ? new DateTime($this->duedate) : null;
+	}
+
+	public function getDuedate($isoFormat = false): ?string {
+		$dt = $this->getDueDateTime();
+		$format = 'c';
 		if (!$isoFormat && $this->databaseType === 'mysql') {
-			return $dt->format('Y-m-d H:i:s');
+			$format = 'Y-m-d H:i:s';
 		}
-		return $dt->format('c');
+
+		return $dt ? $dt->format($format) : null;
 	}
 
 	public function getCalendarObject(): VCalendar {
diff --git a/lib/Model/CardDetails.php b/lib/Model/CardDetails.php
index 08da0ff67..57e246450 100644
--- a/lib/Model/CardDetails.php
+++ b/lib/Model/CardDetails.php
@@ -59,7 +59,7 @@ class CardDetails extends Card
 		$today = new DateTime();
 		$today->setTime(0, 0);
 
-		$match_date = new DateTime($this->getDuedate());
+		$match_date = $this->getDueDateTime() ?? new DateTime();
 		$match_date->setTime(0, 0);
 
 		$diff = $today->diff($match_date);