diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f08ebc..092bcc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## master
 
+- Fix implicit authorization target in anonymous controllers. ([@palkan][])
+
 - Improve default `ActionPolicy::Unauthorized` error message. ([@Spone][])
 
 Before: `Not Authorized` / After: `Not authorized: UserPolicy#create? returns false`
diff --git a/lib/action_policy/rails/controller.rb b/lib/action_policy/rails/controller.rb
index d1b1294..db95a0f 100644
--- a/lib/action_policy/rails/controller.rb
+++ b/lib/action_policy/rails/controller.rb
@@ -56,7 +56,7 @@ def authorize!(record = :__undef__, to: nil, **options)
     # Tries to infer the resource class from controller name
     # (i.e. `controller_name.classify.safe_constantize`).
     def implicit_authorization_target
-      controller_name.classify.safe_constantize
+      controller_name&.classify&.safe_constantize
     end
 
     def verify_authorized
diff --git a/test/action_policy/rails/controllers_test.rb b/test/action_policy/rails/controllers_test.rb
index 402641c..0b81461 100644
--- a/test/action_policy/rails/controllers_test.rb
+++ b/test/action_policy/rails/controllers_test.rb
@@ -274,3 +274,36 @@ def test_index_authorized
     assert_equal "OK", response.body
   end
 end
+
+class TestAnonymousControllerIntegration < ActionController::TestCase
+  class UserPolicy < ::UserPolicy
+    authorize :user, allow_nil: true
+
+    def index? = user.present?
+  end
+
+  def test_nameless_controllers_work
+    controller_class = Class.new(ActionController::Base) do
+      authorize :user, through: :current_user
+
+      def index
+        authorize! with: UserPolicy
+        head :ok
+      end
+
+      def current_user
+        return unless params[:user]
+        @current_user ||= User.new(params[:user])
+      end
+    end
+
+    env = Rack::MockRequest.env_for("http://localhost:3000")
+
+    assert_raises(ActionPolicy::Unauthorized) do
+      controller_class.action(:index).call(env)
+    end
+
+    env = Rack::MockRequest.env_for("http://localhost:3000/?user=guest")
+    controller_class.action(:index).call(env)
+  end
+end