diff --git a/src/danog/MadelineProto/Logger.php b/src/danog/MadelineProto/Logger.php
index 511bf4e0..658b85ee 100644
--- a/src/danog/MadelineProto/Logger.php
+++ b/src/danog/MadelineProto/Logger.php
@@ -117,7 +117,7 @@ class Logger
         self::$colors[self::ERROR] = implode(';', [self::foreground['white'], self::set['bold'], self::background['red']]);
         self::$colors[self::FATAL_ERROR] = implode(';', [self::foreground['red'], self::set['bold'], self::background['light_gray']]);
         try {
-            self::$isatty = posix_isatty(STDOUT);
+            self::$isatty = defined('STDOUT') && posix_isatty(STDOUT);
         } catch (\danog\MadelineProto\Exception $e) {
         }
     }