diff --git a/src/applications/auth/controller/oauth/PhabricatorOAuthLoginController.php b/src/applications/auth/controller/oauth/PhabricatorOAuthLoginController.php
index 4a14e3b0a1..21697101e7 100644
--- a/src/applications/auth/controller/oauth/PhabricatorOAuthLoginController.php
+++ b/src/applications/auth/controller/oauth/PhabricatorOAuthLoginController.php
@@ -255,7 +255,7 @@ final class PhabricatorOAuthLoginController
       'code'          => $code,
     ) + $provider->getExtraTokenParameters();
 
-    $post_data = http_build_query($query_data);
+    $post_data = http_build_query($query_data, '', '&');
     $post_length = strlen($post_data);
 
     $stream_context = stream_context_create(