diff --git a/tasks/6to5.js b/tasks/6to5.js
index fac2cf4..69c42c6 100644
--- a/tasks/6to5.js
+++ b/tasks/6to5.js
@@ -13,7 +13,7 @@ module.exports = function (grunt) {
 			grunt.file.write(el.dest, res.code);
 
 			if (res.map) {
-				grunt.file.write(el.dest + '.map', res.map);
+				grunt.file.write(el.dest + '.map', JSON.stringify(res.map));
 			}
 		});
 	});