diff --git a/src/applications/files/storage/PhabricatorFile.php b/src/applications/files/storage/PhabricatorFile.php
--- a/src/applications/files/storage/PhabricatorFile.php
+++ b/src/applications/files/storage/PhabricatorFile.php
@@ -648,10 +648,17 @@
           // just bail out.
           throw $status;
         } else {
-          // This is HTTP 2XX, so use the response body to save the
-          // file data.
+          // This is HTTP 2XX, so use the response body to save the file data.
+          // Provide a default name based on the URI, truncating it if the URI
+          // is exceptionally long.
+
+          $default_name = basename($uri);
+          $default_name = id(new PhutilUTF8StringTruncator())
+            ->setMaximumBytes(64)
+            ->truncateString($default_name);
+
           $params = $params + array(
-            'name' => basename($uri),
+            'name' => $default_name,
           );
 
           return self::newFromFileData($body, $params);