diff --git a/README.md b/README.md
index ef667e3..17c9a35 100644
--- a/README.md
+++ b/README.md
@@ -128,6 +128,8 @@ class Post extends authorize(Model) {
 }
 ```
 
+(Again, for now the only supported `library` value is `casl`)
+
 ### Options
 
 You can pass an _optional_ options object as the third parameter during initialization. The default values are as follows:
diff --git a/src/index.js b/src/index.js
index 165fef1..9af0e6c 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,6 @@
 const pick = require('lodash/pick')
 const merge = require('lodash/merge')
+const isString = require('lodash/isString')
 
 // TODO: @sssss465 I mean like this kind of shit
 async function fillResourceContext(args) {
@@ -11,8 +12,8 @@ async function fillResourceContext(args) {
   args.context._authorize = OGValue
 }
 
-module.exports = (acl, library = 'role-acl', opts) => {
-  if (!acl || typeof library === 'object') {
+module.exports = (acl, library, opts) => {
+  if (!acl || !isString(library)) {
     throw new Error(
       "usage: require('objection-authorize')(acl, library: String[, opts: Object])(Model)"
     )