diff --git a/package.json b/package.json
index 5baaae7..265e875 100644
--- a/package.json
+++ b/package.json
@@ -36,7 +36,7 @@
   },
   "dependencies": {
     "underscore": "~1.3.3",
-    "mapnik-reference": "~3.1.0",
+    "mapnik-reference": "~3.1.0 || ~4.0.3",
     "xml2js": "~0.1.13"
   },
   "devDependencies": {