diff --git a/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php b/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php
deleted file mode 100644
index b79aa6d..0000000
--- a/core/lib/Drupal/Core/Entity/Plugin/DataType/MapItem.php
+++ /dev/null
@@ -1,66 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Entity\Plugin\DataType\MapItem.
- */
-
-namespace Drupal\Core\Entity\Plugin\DataType;
-
-use Drupal\Core\Annotation\Translation;
-use Drupal\Core\Entity\Field\FieldItemBase;
-use Drupal\Core\TypedData\TypedData;
-
-/**
- * Defines the 'map_field' entity field item.
- *
- * @DataType(
- *   id = "map_field",
- *   label = @Translation("Map field item"),
- *   description = @Translation("An entity field containing a map value."),
- *   list_class = "\Drupal\Core\Entity\Field\FieldItemList"
- * )
- */
-class MapItem extends FieldItemBase {
-
-  /**
-   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
-   *
-   * @param array|null $values
-   *   An array of property values.
-   */
-  public function setValue($values, $notify = TRUE) {
-    $this->values = array();
-    if (!isset($values)) {
-      return;
-    }
-
-    if (!is_array($values)) {
-      if ($values instanceof MapItem) {
-        $values = $values->getValue();
-      }
-      else {
-        $values = unserialize($values);
-      }
-    }
-
-    $this->values = $values;
-  }
-
-  public function __get($name) {
-    if (!isset($this->values[$name])) {
-      $this->values[$name] = array();
-    }
-
-    return $this->values[$name];
-  }
-
-  public function __set($name, $value) {
-    if (isset($value)) {
-      $this->values[$name] = $value;
-    }
-    else {
-      unset($this->values[$name]);
-    }
-  }
-}
diff --git a/core/lib/Drupal/Core/Entity/Plugin/field/field_type/MapItem.php b/core/lib/Drupal/Core/Entity/Plugin/field/field_type/MapItem.php
new file mode 100644
index 0000000..3397b2e
--- /dev/null
+++ b/core/lib/Drupal/Core/Entity/Plugin/field/field_type/MapItem.php
@@ -0,0 +1,69 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Entity\Plugin\field\field_type\MapItem.
+ */
+
+namespace Drupal\Core\Entity\Plugin\field\field_type;
+
+use Drupal\Core\Entity\Field\FieldItemBase;
+
+/**
+ * Defines the 'map' entity field type.
+ *
+ * @FieldType(
+ *   id = "map",
+ *   label = @Translation("Map"),
+ *   description = @Translation("An entity field containing a map value."),
+ *   configurable = FALSE
+ * )
+ */
+class MapItem extends FieldItemBase {
+
+  /**
+   * Overrides \Drupal\Core\Entity\Field\FieldItemBase::setValue().
+   *
+   * @param array|null $values
+   *   An array of property values.
+   */
+  public function setValue($values, $notify = TRUE) {
+    $this->values = array();
+    if (!isset($values)) {
+      return;
+    }
+
+    if (!is_array($values)) {
+      if ($values instanceof MapItem) {
+        $values = $values->getValue();
+      }
+      else {
+        $values = unserialize($values);
+      }
+    }
+
+    $this->values = $values;
+
+    // Notify the parent of any changes.
+    if ($notify && isset($this->parent)) {
+      $this->parent->onChange($this->name);
+    }
+  }
+
+  public function __get($name) {
+    if (!isset($this->values[$name])) {
+      $this->values[$name] = array();
+    }
+
+    return $this->values[$name];
+  }
+
+  public function __set($name, $value) {
+    if (isset($value)) {
+      $this->values[$name] = $value;
+    }
+    else {
+      unset($this->values[$name]);
+    }
+  }
+}