diff --git a/Util_Environment.php b/Util_Environment.php
index 3ea43f9..5c3c214 100644
--- a/Util_Environment.php
+++ b/Util_Environment.php
@@ -115,6 +115,10 @@ static public function url_query( $params = array(), $skip_empty = false,
     static public function filename_to_url( $filename, $use_site_url = false ) {
 		
         $document_root = Util_Environment::document_root();
+        
+        if ( DIRECTORY_SEPARATOR != '/' ){
+        	$filename = str_replace(DIRECTORY_SEPARATOR, '/', $filename);
+        }
 		
         if ( substr( $filename, 0, strlen( $document_root ) ) != $document_root ){
             return '';
@@ -122,10 +126,6 @@ static public function filename_to_url( $filename, $use_site_url = false ) {
 		
         $uri_from_document_root = substr($filename, strlen($document_root) - strlen($filename));
 		
-        if ( DIRECTORY_SEPARATOR != '/' ){
-            $uri_from_document_root = str_replace( DIRECTORY_SEPARATOR, '/', $uri_from_document_root);
-        }
-		
         $url = home_url($uri_from_document_root);
         $url = apply_filters( 'w3tc_filename_to_url', $url );