diff --git a/lib/puma/acme/middleware.rb b/lib/puma/acme/middleware.rb
index 71204a9..d49ba83 100644
--- a/lib/puma/acme/middleware.rb
+++ b/lib/puma/acme/middleware.rb
@@ -3,16 +3,18 @@
 module Puma
   module Acme
     # ACME challenge response handler for HTTP-01 challenges.
-    class Middleware < Sinatra::Base
+    class Middleware
       def initialize(app, manager:)
         @app = app
         @manager = manager
+      end
 
-        super(app)
+      def call(env)
+        dup._call(env)
       end
 
-      get '/.well-known/acme-challenge/:token' do
-        if (token = params[:token]).nil?
+      def _call(env)
+        if (token = token(env)).nil?
           return @app.call(env)
         end
 
@@ -20,8 +22,18 @@ def initialize(app, manager:)
           return @app.call(env)
         end
 
-        content_type 'text/plain'
-        answer.value
+        [200, {'content-type' => 'text/plain;charset=utf-8'}, [answer.value]]
+      end
+
+      private
+
+      def token(env)
+        path = ::Rack::Request.new(env).path_info
+
+        prefix = '/.well-known/acme-challenge/'
+        if path.start_with?(prefix)
+          path[prefix.size..-1]
+        end
       end
     end
   end