diff --git a/core/lib/Drupal/Core/Entity/EntityDisplayModeBase.php b/core/lib/Drupal/Core/Entity/EntityDisplayModeBase.php
index 01fefaf..bc7e7f7 100644
--- a/core/lib/Drupal/Core/Entity/EntityDisplayModeBase.php
+++ b/core/lib/Drupal/Core/Entity/EntityDisplayModeBase.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
 
 /**
- * Base class for config entity types that hold settings for form and view modes.
+ * Base class for config entity types with settings for form and view modes.
  */
 abstract class EntityDisplayModeBase extends ConfigEntityBase implements EntityDisplayModeInterface {
 
@@ -20,14 +20,14 @@
    *
    * @var string
    */
-  public $id;
+  protected $id;
 
   /**
    * The human-readable name of the form or view mode.
    *
    * @var string
    */
-  public $label;
+  protected $label;
 
   /**
    * The entity type this form or view mode is used for.
@@ -37,7 +37,7 @@
    *
    * @var string
    */
-  public $targetEntityType;
+  protected $targetEntityType;
 
   /**
    * Whether or not this form or view mode has custom settings by default.
@@ -56,7 +56,7 @@
    *
    * @var bool
    */
-  public $cache = TRUE;
+  protected $cache = TRUE;
 
   /**
    * {@inheritdoc}
@@ -81,6 +81,14 @@ public function getTargetType() {
   /**
    * {@inheritdoc}
    */
+  public function setTargetType($target_entity_type) {
+    $this->targetEntityType = $target_entity_type;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function calculateDependencies() {
     parent::calculateDependencies();
     $target_entity_type = \Drupal::entityManager()->getDefinition($this->targetEntityType);
diff --git a/core/lib/Drupal/Core/Entity/EntityDisplayModeInterface.php b/core/lib/Drupal/Core/Entity/EntityDisplayModeInterface.php
index bf21c93..e8ad7da 100644
--- a/core/lib/Drupal/Core/Entity/EntityDisplayModeInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityDisplayModeInterface.php
@@ -22,4 +22,14 @@
    */
   public function getTargetType();
 
+  /**
+   * Set the entity type this display mode is used for.
+   *
+   * @param string $target_entity_type
+   *   The target entity type for this display mode.
+   *
+   * @return Drupal\Core\Entity\EntityDisplayModeInterface
+   *   The display mode object, for fluent interface.
+   */
+  public function setTargetType($target_entity_type);
 }
diff --git a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
index cd207de..24b32e0 100644
--- a/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
+++ b/core/modules/field_ui/src/Form/EntityDisplayModeAddForm.php
@@ -53,7 +53,7 @@ protected function prepareEntity() {
       throw new NotFoundHttpException();
     }
 
-    $this->entity->targetEntityType = $this->targetEntityTypeId;
+    $this->entity->setTargetType($this->targetEntityTypeId);
   }
 
 }
diff --git a/core/modules/field_ui/src/Form/EntityFormModeAddForm.php b/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
index d7864ca..869d6b5 100644
--- a/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
+++ b/core/modules/field_ui/src/Form/EntityFormModeAddForm.php
@@ -23,7 +23,7 @@ protected function prepareEntity() {
       throw new NotFoundHttpException();
     }
 
-    $this->entity->targetEntityType = $this->targetEntityTypeId;
+    $this->entity->setTargetType($this->targetEntityTypeId);
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Config/Entity/EntityDisplayModeBaseUnitTest.php b/core/tests/Drupal/Tests/Core/Config/Entity/EntityDisplayModeBaseUnitTest.php
index 4e62f11..67db134 100644
--- a/core/tests/Drupal/Tests/Core/Config/Entity/EntityDisplayModeBaseUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Config/Entity/EntityDisplayModeBaseUnitTest.php
@@ -70,7 +70,6 @@ protected function setUp() {
     $container->set('entity.manager', $this->entityManager);
     $container->set('uuid', $this->uuid);
     \Drupal::setContainer($container);
-
   }
 
   /**
@@ -101,7 +100,62 @@ public function testCalculateDependencies() {
 
     $dependencies = $this->entity->calculateDependencies();
     $this->assertContains('test_module', $dependencies['module']);
+  }
+
+  /**
+   * @covers ::setTargetType
+   */
+  public function testSetTargetType() {
+    // Generate mock.
+    $mock = $this->getMock(
+      'Drupal\Core\Entity\EntityDisplayModeBase',
+      NULL,
+      array(array('something' => 'nothing'), 'test_type')
+    );
+
+    // Some test values.
+    $bad_target = 'uninitialized';
+    $target = 'test_target_type';
+
+    // Gain access to the protected property.
+    $property = new \ReflectionProperty($mock, 'targetEntityType');
+    $property->setAccessible(TRUE);
+    // Set the property to a known state.
+    $property->setValue($mock, $bad_target);
+
+    // Set the target type.
+    $mock->setTargetType($target);
+
+    // Test the outcome.
+    $this->assertNotEquals($bad_target, $property->getValue($mock));
+    $this->assertEquals($target, $property->getValue($mock));
+  }
 
+  /**
+   * @covers ::getTargetType
+   */
+  public function testGetTargetType() {
+    // Generate mock.
+    $mock = $this->getMock(
+      'Drupal\Core\Entity\EntityDisplayModeBase',
+      NULL,
+      array(array('something' => 'nothing'), 'test_type')
+    );
+
+    // A test value.
+    $target = 'test_target_type';
+
+    // Gain access to the protected property.
+    $property = new \ReflectionProperty($mock, 'targetEntityType');
+    $property->setAccessible(TRUE);
+    // Set the property to a known state.
+    $property->setValue($mock, $target);
+
+    // Get the target type.
+    $value = $mock->getTargetType($target);
+
+    // Test the outcome.
+    $this->assertEquals($value, $property->getValue($mock));
   }
 
 }