diff --git a/core/modules/field/lib/Drupal/field/Entity/Field.php b/core/modules/field/lib/Drupal/field/Entity/Field.php
index 9af2a3b..3d9f6a1 100644
--- a/core/modules/field/lib/Drupal/field/Entity/Field.php
+++ b/core/modules/field/lib/Drupal/field/Entity/Field.php
@@ -756,6 +756,10 @@ public function hasData() {
 
   /**
    * Implements the magic __sleep() method.
+   *
+   * Using the Serialize interface and serialize() / unserialize() methods
+   * breaks entity forms in PHP 5.4.
+   * @todo Investigate in https://drupal.org/node/2074253.
    */
   public function __sleep() {
     // Only serialize properties from getExportProperties().
diff --git a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
index f5c467f..c954345 100644
--- a/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
+++ b/core/modules/field/lib/Drupal/field/Entity/FieldInstance.php
@@ -647,6 +647,10 @@ public function offsetUnset($offset) {
 
   /**
    * Implements the magic __sleep() method.
+   *
+   * Using the Serialize interface and serialize() / unserialize() methods
+   * breaks entity forms in PHP 5.4.
+   * @todo Investigate in https://drupal.org/node/2074253.
    */
   public function __sleep() {
     // Only serialize properties from getExportProperties().