diff --git a/lib/plug_image_processing/middlewares/signature_key.ex b/lib/plug_image_processing/middlewares/signature_key.ex
index 50fe139..a0af760 100644
--- a/lib/plug_image_processing/middlewares/signature_key.ex
+++ b/lib/plug_image_processing/middlewares/signature_key.ex
@@ -14,6 +14,8 @@ defmodule PlugImageProcessing.Middlewares.SignatureKey do
       |> Map.drop(["sign"])
       |> URI.encode_query()
 
+    IO.inspect(url_path <> url_query)
+
     Base.url_encode64(:crypto.mac(:hmac, :sha256, config.url_signature_key, url_path <> url_query))
   end
 
diff --git a/test/plug_image_processing/plug_image_processing_test.exs b/test/plug_image_processing/plug_image_processing_test.exs
index 449be8d..8bdcb3f 100644
--- a/test/plug_image_processing/plug_image_processing_test.exs
+++ b/test/plug_image_processing/plug_image_processing_test.exs
@@ -15,5 +15,19 @@ defmodule PlugImageProcessingTest do
 
       assert url === "http://example.com/imageproxy/resize?url=http%3A%2F%2Fbucket.com%2Ftest.jpg&width=10"
     end
+
+    test "valid with signature", %{config: config} do
+      url_signature_key = "12345"
+      config = Keyword.put(config, :url_signature_key, url_signature_key)
+
+      url = PlugImageProcessing.generate_url("http://example.com", config, :resize, %{url: "http://bucket.com/test.jpg", width: 10})
+
+      assert url ===
+               "http://example.com/imageproxy/resize?url=http%3A%2F%2Fbucket.com%2Ftest.jpg&width=10&sign=#{generate_signature_from_url(url_signature_key, "resizeurl=http%3A%2F%2Fbucket.com%2Ftest.jpg&width=10")}"
+    end
+  end
+
+  defp generate_signature_from_url(url_signature_key, url) do
+    Base.url_encode64(:crypto.mac(:hmac, :sha256, url_signature_key, url))
   end
 end