diff --git a/src/Plugin/Field/FieldType/SmartDateListItemBase.php b/src/Plugin/Field/FieldType/SmartDateListItemBase.php
index 697de7c..7abb22e 100644
--- a/src/Plugin/Field/FieldType/SmartDateListItemBase.php
+++ b/src/Plugin/Field/FieldType/SmartDateListItemBase.php
@@ -14,6 +14,9 @@ abstract class SmartDateListItemBase extends ListItemBase {
    * {@inheritdoc}
    */
   public static function parseValues($values) {
+    if (is_array($values)) {
+      $values = implode("\n", $values);
+    }
     // Use the ListItemBase parsing function, but don't allow generated keys.
     if (!class_exists(DeprecationHelper::class)) {
       return static::extractAllowedValues($values, 1);