diff --git a/src/future/oauth/PhutilOAuth1Future.php b/src/future/oauth/PhutilOAuth1Future.php
--- a/src/future/oauth/PhutilOAuth1Future.php
+++ b/src/future/oauth/PhutilOAuth1Future.php
@@ -268,7 +268,8 @@
           throw new Exception(pht('%s failed!', 'openssl_sign()'));
         }
 
-        openssl_free_key($pkey);
+        // Deprecated in PHP 8; key is automatically freed.
+        @openssl_free_key($pkey);
 
         return base64_encode($signature);
       case 'PLAINTEXT':