diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index da0bc47..376cfd8 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -340,7 +340,11 @@ protected function buildBaseFieldDefinitions($entity_type_id) {
     $base_field_definitions = $class::baseFieldDefinitions($entity_type);
     $provider = $entity_type->getProvider();
     foreach ($base_field_definitions as $definition) {
-      $definition->setProvider($provider);
+      // @todo Remove this check one FieldDefinitionInterface exposes a proper
+      //   provider setter. See https://drupal.org/node/2225961.
+      if ($definition instanceof FieldDefinition) {
+        $definition->setProvider($provider);
+      }
     }
 
     // Retrieve base field definitions from modules.
@@ -350,7 +354,11 @@ protected function buildBaseFieldDefinitions($entity_type_id) {
         // Ensure the provider key actually matches the name of the provider
         // defining the field.
         foreach ($module_definitions as $field_name => $definition) {
-          $definition->setProvider($module);
+          // @todo Remove this check one FieldDefinitionInterface exposes a
+          //   proper provider setter. See https://drupal.org/node/2225961.
+          if ($definition instanceof FieldDefinition) {
+            $definition->setProvider($module);
+          }
           $base_field_definitions[$field_name] = $definition;
         }
       }
@@ -429,7 +437,11 @@ protected function buildBundleFieldDefinitions($entity_type_id, $bundle, array $
     $provider = $entity_type->getProvider();
     $bundle_field_definitions = $class::bundleFieldDefinitions($entity_type, $bundle, $base_field_definitions);
     foreach ($bundle_field_definitions as $definition) {
-      $definition->setProvider($provider);
+      // @todo Remove this check one FieldDefinitionInterface exposes a proper
+      //   provider setter. See https://drupal.org/node/2225961.
+      if ($definition instanceof FieldDefinition) {
+        $definition->setProvider($provider);
+      }
     }
 
     // Retrieve base field definitions from modules.
@@ -439,7 +451,11 @@ protected function buildBundleFieldDefinitions($entity_type_id, $bundle, array $
         // Ensure the provider key actually matches the name of the provider
         // defining the field.
         foreach ($module_definitions as $field_name => $definition) {
-          $definition->setProvider($module);
+          // @todo Remove this check one FieldDefinitionInterface exposes a
+          //   proper provider setter. See https://drupal.org/node/2225961.
+          if ($definition instanceof FieldDefinition) {
+            $definition->setProvider($module);
+          }
           $bundle_field_definitions[$field_name] = $definition;
         }
       }
diff --git a/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
index b58336f..5c82343 100644
--- a/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php
@@ -562,7 +562,10 @@ public function testGetFieldDefinitionsProvider() {
 
     $module = 'entity_manager_test_module';
 
-    $field_definition = $this->getMockBuilder('Drupal\Core\Field\FieldDefinitionInterface')
+    // @todo Mock FieldDefinitionInterface once it exposes a proper provider
+    //   setter. See https://drupal.org/node/2225961.
+    $field_definition = $this->getMockBuilder('Drupal\Core\Field\FieldDefinition')
+      ->disableOriginalConstructor()
       ->getMock();
 
     // We expect two calls as the field definition will be returned from both