diff --git a/uuid.core.inc b/uuid.core.inc
index f893ff1..13a889c 100644
--- a/uuid.core.inc
+++ b/uuid.core.inc
@@ -126,7 +126,16 @@ function file_entity_uuid_presave(&$entity, $entity_type) {
   if ($entity_type == 'file') {
     entity_property_uuid_to_id($entity, 'user', 'uid');
 
+    // Write the new file to the local filesystem.
     if (isset($entity->file_contents)) {
+      // Don't try to write it if it uses a stream wrapper that isn't writeable
+      // (for example, if it is a remotely-hosted video).
+      $scheme = file_uri_scheme($entity->uri);
+      $wrappers = file_get_stream_wrappers(STREAM_WRAPPERS_WRITE);
+      if (empty($wrappers[$scheme])) {
+        return;
+      }
+
       // Check for an existing file with the same URI.
       $existing_files = file_load_multiple(array(), array('uri' => $entity->uri));
       $existing = (object) array('uri' => NULL, 'uuid' => NULL);