diff --git imagecache/imagecache.module imagecache/imagecache.module
index 1584304..6f6af7e 100644
--- imagecache/imagecache.module
+++ imagecache/imagecache.module
@@ -341,7 +341,7 @@ function imagecache_action_definition($action) {
  *   A Boolean indicating that the URL should be absolute. Defaults to TRUE.
  */
 function imagecache_create_url($presetname, $filepath, $bypass_browser_cache = FALSE, $absolute = TRUE) {
-  $args = array('query' => empty($bypass_browser_cache) ? NULL : time());
+  $args = array('query' => empty($bypass_browser_cache) ? filemtime($filepath) : time());
   $file_directory = file_directory_path();
 
   // Determine the path of the derivative inside the files directory.