diff --git a/src/future/oauth/PhutilOAuth1Future.php b/src/future/oauth/PhutilOAuth1Future.php
index f73b9db0..87a819d9 100644
--- a/src/future/oauth/PhutilOAuth1Future.php
+++ b/src/future/oauth/PhutilOAuth1Future.php
@@ -225,11 +225,12 @@ final class PhutilOAuth1Future extends FutureProxy {
 
   private function signString($string) {
     $consumer_secret = null;
+    $key = '';
     if ($this->consumerSecret) {
       $consumer_secret = $this->consumerSecret->openEnvelope();
+      $key .= urlencode($consumer_secret).'&';
     }
 
-    $key = urlencode($consumer_secret).'&';
     if ($this->tokenSecret !== null) {
       $key .= urlencode($this->tokenSecret);
     }