diff --git a/src/PointInTime.php b/src/PointInTime.php
index 8ce2c41..b3a22aa 100644
--- a/src/PointInTime.php
+++ b/src/PointInTime.php
@@ -303,6 +303,6 @@ private static function dateInterval(Period $period): ?\DateInterval
         }
 
         /** @psalm-suppress ImpureMethodCall */
-        return \DateInterval::createFromDateString(\implode(' + ', $parts));
+        return \DateInterval::createFromDateString(\implode(' + ', $parts)) ?: null;
     }
 }