diff --git a/src/NodaSplitTime.php b/src/NodaSplitTime.php
index 1448365..1228ffe 100644
--- a/src/NodaSplitTime.php
+++ b/src/NodaSplitTime.php
@@ -338,11 +338,13 @@ final class NodaSplitTime {
         // Calculate start date and end date
         if (($this->before_after_indicator === NodaTimeBeforeAfterIndicator::before
             || $this->before_after_indicator === NodaTimeBeforeAfterIndicator::until)
+            || $start_date === '?'
         ) {
             $this->start_date = '-9999-12-31';
         }
         if (($this->before_after_indicator === NodaTimeBeforeAfterIndicator::after
             || $this->before_after_indicator === NodaTimeBeforeAfterIndicator::since)
+            || $end_date === '?'
         ) {
             $this->end_date = '9999-12-31';
         }