diff --git a/CHANGES.md b/CHANGES.md
index 1dac4cd..e8eaf32 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,3 +1,9 @@
+### 2.2.0 (2017-08-31)
+
+* [#46](https://github.com/square/rails-auth/pull/46)
+  Add linting for YAML acl checks (i.e. prevent duplicate keys)
+  ([@cgthornt])
+
 ### 2.1.3 (2017-08-04)
 
 * [#44](https://github.com/square/rails-auth/pull/44)
diff --git a/lib/rails/auth/acl.rb b/lib/rails/auth/acl.rb
index e6d7a2f..bad3b61 100644
--- a/lib/rails/auth/acl.rb
+++ b/lib/rails/auth/acl.rb
@@ -17,6 +17,15 @@ class ACL
       # @param [String] :yaml serialized YAML to load an ACL from
       def self.from_yaml(yaml, **args)
         require "yaml"
+        require "yamllint"
+
+        linter = YamlLint::Linter.new
+        linter.check_stream(StringIO.new(yaml))
+        if linter.errors?
+          # Always in the format of {"" => ["msg1", "msg2", ...]}
+          msg = linter.errors[""].join(", ")
+          raise ParseError, "ACL lint failed: #{msg}"
+        end
         new(YAML.load(yaml), **args)
       end
 
diff --git a/lib/rails/auth/version.rb b/lib/rails/auth/version.rb
index 9b846bb..de5e78b 100644
--- a/lib/rails/auth/version.rb
+++ b/lib/rails/auth/version.rb
@@ -3,6 +3,6 @@
 module Rails
   # Pluggable authentication and authorization for Rack/Rails
   module Auth
-    VERSION = "2.1.3".freeze
+    VERSION = "2.2.0".freeze
   end
 end
diff --git a/rails-auth.gemspec b/rails-auth.gemspec
index 368f050..a96d4d5 100644
--- a/rails-auth.gemspec
+++ b/rails-auth.gemspec
@@ -28,6 +28,7 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = ">= 2.0.0"
 
   spec.add_runtime_dependency "rack"
+  spec.add_runtime_dependency "yamllint", "~> 0.0.9"
 
   spec.add_development_dependency "bundler", "~> 1.10"
   spec.add_development_dependency "rake", "~> 10.0"
diff --git a/spec/fixtures/example_invalid_acl.yml b/spec/fixtures/example_invalid_acl.yml
new file mode 100644
index 0000000..66958aa
--- /dev/null
+++ b/spec/fixtures/example_invalid_acl.yml
@@ -0,0 +1,7 @@
+---
+- resources:
+  - method: ALL
+    method: POST
+    path: /foo/bar/.*
+  - path: /foo/bar
+    path: /bar
diff --git a/spec/rails/auth/acl_spec.rb b/spec/rails/auth/acl_spec.rb
index 3bde83c..599c864 100644
--- a/spec/rails/auth/acl_spec.rb
+++ b/spec/rails/auth/acl_spec.rb
@@ -31,4 +31,17 @@
       expect(resources.first.path).to eq %r{\A/foo/bar/.*\z}
     end
   end
+
+  describe ".from_yaml" do
+    subject { example_acl }
+
+    context "when given an invalid YAML file" do
+      let(:example_config) { fixture_path("example_invalid_acl.yml").read }
+
+      it "raises an error" do
+        expect { subject }.to raise_error Rails::Auth::ParseError,
+          'ACL lint failed: The same key is defined more than once: 0.resources.0.method, The same key is defined more than once: 0.resources.1.path'
+      end
+    end
+  end
 end