diff --git a/xhprof_lib/utils/xhprof_runs.php b/xhprof_lib/utils/xhprof_runs.php
index cde5ff55..94167214 100644
--- a/xhprof_lib/utils/xhprof_runs.php
+++ b/xhprof_lib/utils/xhprof_runs.php
@@ -96,7 +96,7 @@ public function __construct($dir = null) {
       if (empty($dir)) {
 
         // some default that at least works on unix...
-        $dir = "/tmp";
+        $dir = sys_get_temp_dir();
 
         xhprof_error("Warning: Must specify directory location for XHProf runs. ".
                      "Trying {$dir} as default. You can either pass the " .