diff --git a/src/aws/auth.coffee b/src/aws/auth.coffee
index 40437d9..ec78935 100644
--- a/src/aws/auth.coffee
+++ b/src/aws/auth.coffee
@@ -112,8 +112,8 @@ class AwsAuth
       @pad(@date.getUTCSeconds()) + "Z"
 
   timeStampYYYYMMDD: ->
-    @date.getUTCFullYear() +
-      @pad(@date.getUTCMonth() + 1) +
-      @pad(@date.getUTCDate())
+    "#{@date.getUTCFullYear()}" +
+      "#{@pad(@date.getUTCMonth() + 1)}" +
+      "#{@pad(@date.getUTCDate())}"
 
-export default AwsAuth
\ No newline at end of file
+export default AwsAuth