diff --git a/package.json b/package.json
index 507370d..549ec13 100755
--- a/package.json
+++ b/package.json
@@ -7,12 +7,15 @@
     "url": "https://github.com/KorAP/Kalamar.git"
   },
   "devDependencies": {
-    "grunt":                   "~0.4.5",
+    "grunt":                   "^0.4.5",
     "grunt-contrib-copy":      "^0.8.0",
-    "grunt-contrib-imagemin":  "^0.9.4",
+    "grunt-contrib-imagemin":  "^1.0.0",
+    "imagemin":                "^4.0.0",
     "grunt-contrib-jasmine":   "^0.8.2",
     "grunt-contrib-sass":      "^0.9.2",
     "grunt-contrib-watch":     "^0.6.1",
-    "grunt-contrib-requirejs": "^0.4.4"
+    "grunt-contrib-requirejs": "^0.4.4",
+    "vinyl-fs":                "^2.1.1",
+    "optipng-bin":             "^3.1.2"
   }
 }