diff --git a/promises/index.php b/promises/index.php
index c64cba2..8b9725e 100644
--- a/promises/index.php
+++ b/promises/index.php
@@ -25,6 +25,7 @@ $requests = function ($n) use ($client) {
 
     for ($i = 0; $i < $n; $i++) {
         yield function() use ($client, $uri, $i) {
+            Lib\printf('  yield '. $i);
             return $client->getAsync($uri . http_build_query(['o' => $i, 's' => random_int(1, 5)]));
         };
     }