diff --git a/tasks/cssmin.js b/tasks/cssmin.js
index e0c07c3..354352e 100644
--- a/tasks/cssmin.js
+++ b/tasks/cssmin.js
@@ -38,7 +38,7 @@ module.exports = function (grunt) {
       var compiled = '';
 
       options.target = file.dest;
-      options.relativeTo = path.dirname(availableFiles[0]);
+      options.relativeTo = path.dirname(availableFiles[0] || '');
 
       try {
         compiled = new CleanCSS(options).minify(availableFiles);