diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index 0adfb7ed3d8..accd0368002 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -8047,7 +8047,7 @@ function remove_dir($dir, $content_only=false) {
 function check_dir_exists($dir, $create=false, $recursive=false) {
     global $CFG;
 
-    if (strstr($dir, $CFG->dataroot.'/') === false) {
+    if (strstr(cleardoubleslashes($dir), cleardoubleslashes($CFG->dataroot.'/')) === false) {
         debugging('Warning. Wrong call to check_dir_exists(). $dir must be an absolute path under $CFG->dataroot ("' . $dir . '" is incorrect)', DEBUG_DEVELOPER);
     }