diff --git a/src/Plugin/Field/FieldWidget/DateRecurModularAlphaWidget.php b/src/Plugin/Field/FieldWidget/DateRecurModularAlphaWidget.php
index 8fa3ce2..6cda7d8 100644
--- a/src/Plugin/Field/FieldWidget/DateRecurModularAlphaWidget.php
+++ b/src/Plugin/Field/FieldWidget/DateRecurModularAlphaWidget.php
@@ -281,6 +281,9 @@ class DateRecurModularAlphaWidget extends DateRecurModularWidgetBase {
     /** @var string|null $timeZone */
     $timeZone = $form_state->getValue(array_merge($element['#parents'], ['time_zone']));
 
+    if (($start instanceof DrupalDateTime && $end instanceof DrupalDateTime) && ($start > $end)) {
+      $form_state->setError($element['end'], \t('End date cannot be before the start date.'));
+    }
     if ($start && !$timeZone) {
       $form_state->setError($element['start'], \t('Time zone must be set if start date is set.'));
     }