diff -u b/modules/order/src/Adjustment.php b/modules/order/src/Adjustment.php
--- b/modules/order/src/Adjustment.php
+++ b/modules/order/src/Adjustment.php
@@ -197,20 +197,31 @@
   }
 
   /**
+   * Returns all storage elements as an array.
+   *
+   * @return array
+   *   An associative array of attributes.
+   */
+  public function toArray() {
+    return [
+      'type' => $this->type,
+      'label' => $this->label,
+      'amount' => $this->amount->toArray(),
+      'percentage' => $this->percentage,
+      'sourceId' => $this->sourceId,
+      'included' => $this->included,
+      'locked' => $this->locked,
+    ];
+
+  }
+
+  /**
    * {@inheritdoc}
    *
    * @see \Drupal\serialization\Normalizer\AnyNormalizer
    */
   public function getIterator() {
-    return new \ArrayIterator([
-      'type' => $this->getType(),
-      'label' => $this->getLabel(),
-      'amount' => $this->getAmount(),
-      'percentage' => $this->getPercentage(),
-      'source_id' => $this->getSourceId(),
-      'included' => $this->isIncluded(),
-      'locked' => $this->isLocked(),
-    ]);
+    return new \ArrayIterator($this->toArray());
   }
 
 }
only in patch2:
unchanged:
--- a/modules/order/src/Plugin/Field/FieldType/AdjustmentItem.php
+++ b/modules/order/src/Plugin/Field/FieldType/AdjustmentItem.php
@@ -3,6 +3,7 @@
 namespace Drupal\commerce_order\Plugin\Field\FieldType;
 
 use Drupal\commerce_order\Adjustment;
+use Drupal\commerce_price\Price;
 use Drupal\Core\Field\FieldItemBase;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\TypedData\DataDefinition;
@@ -48,6 +49,11 @@ class AdjustmentItem extends FieldItemBase {
       // The property definition causes the adjustment to be in 'value' key.
       $values = reset($values);
     }
+    // Used for denormalization.
+    if (is_array($values)) {
+      $values['amount'] = new Price($values['amount']['number'], $values['amount']['currency_code']);
+      $values = new Adjustment($values);
+    }
     if (!$values instanceof Adjustment) {
       $values = NULL;
     }