diff --git a/src/Psalm/Internal/Codebase/Functions.php b/src/Psalm/Internal/Codebase/Functions.php
index 5671ecdad58..8b9ad1f9081 100644
--- a/src/Psalm/Internal/Codebase/Functions.php
+++ b/src/Psalm/Internal/Codebase/Functions.php
@@ -411,7 +411,7 @@ public function isCallMapFunctionPure(
             'header', 'header_remove', 'http_response_code', 'setcookie',
 
             // output buffer
-            'ob_start', 'ob_end_clean', 'readfile', 'printf', 'var_dump', 'phpinfo',
+            'ob_start', 'ob_end_clean', 'ob_get_clean', 'readfile', 'printf', 'var_dump', 'phpinfo',
             'ob_implicit_flush', 'vprintf',
 
             // mcrypt