diff --git a/tasks/wkhtmltopdf.js b/tasks/wkhtmltopdf.js
index 6f6dc05..9b37a80 100644
--- a/tasks/wkhtmltopdf.js
+++ b/tasks/wkhtmltopdf.js
@@ -18,7 +18,9 @@ module.exports = function(grunt) {
 
   grunt.registerMultiTask('wkhtmltopdf', 'Your task description goes here.', function() {
 
-    this.files.forEach(function(file) {
+    var done = this.async();
+
+    this.files.forEach(function(file, filesIndex) {
 
       var pathlib = require('path');
       // calculate the destination directory and ensure it exists, since
@@ -30,7 +32,7 @@ module.exports = function(grunt) {
       }
       grunt.file.mkdir(destPath);
 
-      file.src.forEach(function(src) {
+      file.src.forEach(function(src, srcIndex) {
 
         var dest = file.dest;
         // wkhtmltopdf seems to require that the destination be a file
@@ -64,6 +66,10 @@ module.exports = function(grunt) {
             if (err) {
               grunt.log('>>>', err);
             }
+            // if this is the last src of the last file, we are done.
+            if((filesIndex+1 >= files.length) && (srcIndex+1 >= src.length)) {
+              done();
+            }
           }
         });
       });