diff --git a/core/modules/migrate_drupal/src/Plugin/MigrateFieldPluginManagerInterface.php b/core/modules/migrate_drupal/src/Plugin/MigrateFieldPluginManagerInterface.php
index 8bcb050..7219c2b 100644
--- a/core/modules/migrate_drupal/src/Plugin/MigrateFieldPluginManagerInterface.php
+++ b/core/modules/migrate_drupal/src/Plugin/MigrateFieldPluginManagerInterface.php
@@ -5,7 +5,7 @@
 use Drupal\migrate\Plugin\MigratePluginManagerInterface;
 use Drupal\migrate\Plugin\MigrationInterface;
 
-interface MigrateFieldPluginManagerInterface extends MigratePluginManagerInterface  {
+interface MigrateFieldPluginManagerInterface extends MigratePluginManagerInterface {
 
   /**
    * Get the plugin ID from the field type.
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/CckMigration.php b/core/modules/migrate_drupal/src/Plugin/migrate/CckMigration.php
index 6c129a3..a89f072 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/CckMigration.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/CckMigration.php
@@ -8,4 +8,11 @@
  * @deprecated in Drupal 8.2.x, to be removed before Drupal 9.0.x. Use
  * \Drupal\migrate_drupal\Plugin\migrate\FieldMigration instead.
  */
-class CckMigration extends FieldMigration { }
+class CckMigration extends FieldMigration {
+
+  /**
+   * {@inheritdoc}
+   */
+  const PLUGIN_METHOD = 'cck_plugin_method';
+
+}
diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/FieldMigration.php b/core/modules/migrate_drupal/src/Plugin/migrate/FieldMigration.php
index acc4a71..62976db 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/FieldMigration.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/FieldMigration.php
@@ -19,6 +19,17 @@
 class FieldMigration extends Migration implements ContainerFactoryPluginInterface {
 
   /**
+   * Defines which configuration option has the migration processing function.
+   *
+   * Default method is 'field_plugin_method'. For backwards compatibility,
+   * this constant is overridden in the CckMigration class, in order to
+   * fallback to the old 'cck_plugin_method'.
+   *
+   * @const string
+   */
+  const PLUGIN_METHOD = 'field_plugin_method';
+
+  /**
    * Flag indicating whether the field data has been filled already.
    *
    * @var bool
@@ -122,14 +133,7 @@ public function getProcess() {
           if (!isset($this->fieldPluginCache[$field_type])) {
             $this->fieldPluginCache[$field_type] = $this->fieldPluginManager->createInstance($plugin_id, [], $this);
           }
-          if (!empty($this->pluginDefinition['field_plugin_method'])) {
-            $method = $this->pluginDefinition['field_plugin_method'];
-          }
-          else {
-            // For backwards compatibility, fallback to the old
-            // cck_plugin_method.
-            $method = $this->pluginDefinition['cck_plugin_method'];
-          }
+          $method = $this->pluginDefinition[static::PLUGIN_METHOD];
           call_user_func([$this->fieldPluginCache[$field_type], $method], $this);
         }
       }