diff -u b/core/modules/migrate/src/Plugin/migrate/destination/EntityFile.php b/core/modules/migrate/src/Plugin/migrate/destination/EntityFile.php
--- b/core/modules/migrate/src/Plugin/migrate/destination/EntityFile.php
+++ b/core/modules/migrate/src/Plugin/migrate/destination/EntityFile.php
@@ -72,6 +72,15 @@
     $source = $this->configuration['source_base_path'] . $file;
 
     $dirname = $this->fileSystem->dirname($destination);
+    // It's pretty safe to assume that $source exists. $destination, on the
+    // other hand, might not. So we need to do a little dancing to prepare
+    // the destination path. The issue is that, for URIs like public://foo.txt,
+    // FileSystemInterface::dirname() will return public:// -- which will
+    // be roundly rejected by file_prepare_directory(). So if dirname() returned
+    // such a URI, translate it to a path for file_prepare_directory().
+    if (preg_match('#://#', $dirname)) {
+      $dirname = $this->fileSystem->realpath($dirname);
+    }
     if (!file_prepare_directory($dirname, FILE_CREATE_DIRECTORY)) {
       throw new MigrateException(t('Could not create directory %dirname', array('%dirname' => $dirname)));
     }
diff -u b/core/modules/migrate/tests/src/Unit/destination/EntityFileTest.php b/core/modules/migrate/tests/src/Unit/destination/EntityFileTest.php
--- b/core/modules/migrate/tests/src/Unit/destination/EntityFileTest.php
+++ b/core/modules/migrate/tests/src/Unit/destination/EntityFileTest.php
@@ -39,6 +39,7 @@
   public function setUp() {
     parent::setUp();
     $this->destination = new TestEntityFile([]);
+    $this->destination->fileSystem = \Drupal::getContainer()->get('file_system');
 
     $this->installConfig(['system']);
     file_put_contents('/tmp/test-file.jpg', '');
@@ -70,7 +71,7 @@
       [['filepath' => 'core/modules/simpletest/files/image-test.jpg'], 'public://file1.jpg', TRUE, DRUPAL_ROOT . '/'],
       // Test a temporary file using an absolute path.
       [['filepath' => '/tmp/test-file.jpg'], 'temporary://test.jpg', TRUE, ''],
-      // Test a temporary file using an relative path.
+      // Test a temporary file using a relative path.
       [['filepath' => 'test-file.jpg'], 'temporary://core/modules/simpletest/files/test.jpg', TRUE, '/tmp/'],
       // Test a remote path to local.
       [['filepath' => 'core/modules/simpletest/files/image-test.jpg'], 'public://remote-file.jpg', TRUE, $base_url . '/'],
@@ -79,7 +80,6 @@
     ];
   }
 
-
   /**
    * Test that non-existent files throw an exception.
    */
@@ -134,6 +134,11 @@
    */
   public $configuration;
 
+  /**
+   * @var \Drupal\Core\File\FileSystemInterface
+   */
+  public $fileSystem;
+
   public function __construct($configuration) {
     $configuration +=  array(
       'source_base_path' => '',