diff --git a/lib/datadog/tracing/contrib/rack/middlewares.rb b/lib/datadog/tracing/contrib/rack/middlewares.rb
index 0caa839848..550b5f8828 100644
--- a/lib/datadog/tracing/contrib/rack/middlewares.rb
+++ b/lib/datadog/tracing/contrib/rack/middlewares.rb
@@ -268,10 +268,12 @@ def parse_url(env, original_env)
 
                          query_string.empty? ? path : "#{path}?#{query_string}"
                        else
-                         request_uri
+                         # normally REQUEST_URI starts at the path, but it
+                         # might contain the full URL in some cases (e.g WEBrick)
+                         request_uri.sub(/^#{base_url}/, '')
                        end
 
-            ::URI.join(base_url, fullpath).to_s
+            base_url + fullpath
           end
 
           def parse_user_agent_header(headers)
diff --git a/spec/datadog/tracing/contrib/rack/middlewares_spec.rb b/spec/datadog/tracing/contrib/rack/middlewares_spec.rb
index caf3284ef1..ea5b427615 100644
--- a/spec/datadog/tracing/contrib/rack/middlewares_spec.rb
+++ b/spec/datadog/tracing/contrib/rack/middlewares_spec.rb
@@ -44,4 +44,27 @@
       end
     end
   end
+
+  # Non-ASCII URLs cannot be tested with `rack-test` as of v2.0.2.
+  # It would be ideal if that was possible, as we could create integration tests
+  # for such cases.
+  #
+  # As an alternative, we test the parsing method directly.
+  describe '#parse_url' do
+    subject(:parse_url) { middleware.send(:parse_url, env, original_env) }
+    let(:env) { { 'REQUEST_URI' => uri, 'HTTP_HOST' => 'localhost:443', 'rack.url_scheme' => 'https' } }
+    let(:original_env) { {} }
+
+    context 'with Unicode characters' do
+      let(:uri) { 'https://localhost/success/?繋がってて' }
+
+      it { is_expected.to eq(uri) }
+    end
+
+    context 'with unencoded ASCII characters' do
+      let(:uri) { 'https://localhost/success/|' }
+
+      it { is_expected.to eq(uri) }
+    end
+  end
 end