diff --git a/quic/masque/masque_client_session.cc b/quic/masque/masque_client_session.cc
index 79ab509..1a9fc9b 100644
--- a/quic/masque/masque_client_session.cc
+++ b/quic/masque/masque_client_session.cc
@@ -6,6 +6,7 @@
 #include "absl/algorithm/container.h"
 #include "quic/core/http/spdy_utils.h"
 #include "quic/core/quic_data_reader.h"
+#include "quic/core/quic_utils.h"
 #include "common/platform/api/quiche_text_utils.h"
 
 namespace quic {
@@ -198,6 +199,16 @@
 }
 
 void MasqueClientSession::OnStreamClosed(QuicStreamId stream_id) {
+  if (QuicUtils::IsBidirectionalStreamId(stream_id, version()) &&
+      QuicUtils::IsClientInitiatedStreamId(transport_version(), stream_id)) {
+    QuicSpdyClientStream* stream =
+        reinterpret_cast<QuicSpdyClientStream*>(GetActiveStream(stream_id));
+    if (stream != nullptr) {
+      QUIC_DLOG(INFO) << "Stream " << stream_id
+                      << " closed, got response headers:"
+                      << stream->response_headers().DebugString();
+    }
+  }
   for (auto it = connect_udp_client_states_.begin();
        it != connect_udp_client_states_.end();) {
     if (it->stream()->id() == stream_id) {
diff --git a/quic/masque/masque_server_backend.cc b/quic/masque/masque_server_backend.cc
index 64c36e1..6c7f7e1 100644
--- a/quic/masque/masque_server_backend.cc
+++ b/quic/masque/masque_server_backend.cc
@@ -21,20 +21,20 @@
     const spdy::Http2HeaderBlock& request_headers,
     const std::string& request_body,
     QuicSimpleServerBackend::RequestHandler* request_handler) {
-  auto path_pair = request_headers.find(":path");
-  auto method_pair = request_headers.find(":method");
-  auto scheme_pair = request_headers.find(":scheme");
-  if (path_pair == request_headers.end() ||
-      method_pair == request_headers.end() ||
-      scheme_pair == request_headers.end()) {
-    // This request is missing required headers.
-    return false;
-  }
-  absl::string_view path = path_pair->second;
-  absl::string_view scheme = scheme_pair->second;
-  absl::string_view method = method_pair->second;
   std::string masque_path = "";
   if (masque_mode_ == MasqueMode::kLegacy) {
+    auto path_pair = request_headers.find(":path");
+    auto method_pair = request_headers.find(":method");
+    auto scheme_pair = request_headers.find(":scheme");
+    if (path_pair == request_headers.end() ||
+        method_pair == request_headers.end() ||
+        scheme_pair == request_headers.end()) {
+      // This request is missing required headers.
+      return false;
+    }
+    absl::string_view path = path_pair->second;
+    absl::string_view scheme = scheme_pair->second;
+    absl::string_view method = method_pair->second;
     if (scheme != "https" || method != "POST" || request_body.empty()) {
       // MASQUE requests MUST be a non-empty https POST.
       return false;
@@ -45,11 +45,6 @@
       return false;
     }
     masque_path = std::string(path.substr(sizeof("/.well-known/masque/") - 1));
-  } else {
-    if (method != "CONNECT-UDP") {
-      // Unexpected method.
-      return false;
-    }
   }
 
   if (!server_authority_.empty()) {
diff --git a/quic/masque/masque_server_session.cc b/quic/masque/masque_server_session.cc
index 4f065ee..78cbbf4 100644
--- a/quic/masque/masque_server_session.cc
+++ b/quic/masque/masque_server_session.cc
@@ -60,13 +60,13 @@
 
 std::unique_ptr<QuicBackendResponse> CreateBackendErrorResponse(
     absl::string_view status,
-    absl::string_view body) {
+    absl::string_view error_details) {
   spdy::Http2HeaderBlock response_headers;
   response_headers[":status"] = status;
+  response_headers["masque-debug-info"] = error_details;
   auto response = std::make_unique<QuicBackendResponse>();
   response->set_response_type(QuicBackendResponse::REGULAR_RESPONSE);
   response->set_headers(std::move(response_headers));
-  response->set_body(body);
   return response;
 }
 
@@ -177,12 +177,21 @@
     auto scheme_pair = request_headers.find(":scheme");
     auto method_pair = request_headers.find(":method");
     auto authority_pair = request_headers.find(":authority");
-    if (path_pair == request_headers.end() ||
-        scheme_pair == request_headers.end() ||
-        method_pair == request_headers.end() ||
-        authority_pair == request_headers.end()) {
-      QUIC_DLOG(ERROR) << "MASQUE request is missing required headers";
-      return CreateBackendErrorResponse("400", "Missing required headers");
+    if (path_pair == request_headers.end()) {
+      QUIC_DLOG(ERROR) << "MASQUE request is missing :path";
+      return CreateBackendErrorResponse("400", "Missing :path");
+    }
+    if (scheme_pair == request_headers.end()) {
+      QUIC_DLOG(ERROR) << "MASQUE request is missing :scheme";
+      return CreateBackendErrorResponse("400", "Missing :scheme");
+    }
+    if (method_pair == request_headers.end()) {
+      QUIC_DLOG(ERROR) << "MASQUE request is missing :method";
+      return CreateBackendErrorResponse("400", "Missing :method");
+    }
+    if (authority_pair == request_headers.end()) {
+      QUIC_DLOG(ERROR) << "MASQUE request is missing :authority";
+      return CreateBackendErrorResponse("400", "Missing :authority");
     }
     absl::string_view path = path_pair->second;
     absl::string_view scheme = scheme_pair->second;
diff --git a/quic/tools/quic_memory_cache_backend.cc b/quic/tools/quic_memory_cache_backend.cc
index c67e5b3..c030732 100644
--- a/quic/tools/quic_memory_cache_backend.cc
+++ b/quic/tools/quic_memory_cache_backend.cc
@@ -316,8 +316,13 @@
     quic_response = GetResponse(authority->second, path->second);
   }
 
-  std::string request_url =
-      std::string(authority->second) + std::string(path->second);
+  std::string request_url;
+  if (authority != request_headers.end()) {
+    request_url = std::string(authority->second);
+  }
+  if (path != request_headers.end()) {
+    request_url += std::string(path->second);
+  }
   std::list<ServerPushInfo> resources = GetServerPushResources(request_url);
   QUIC_DVLOG(1)
       << "Fetching QUIC response from backend in-memory cache for url "
diff --git a/quic/tools/quic_simple_server_stream.cc b/quic/tools/quic_simple_server_stream.cc
index 800608b..4377b56 100644
--- a/quic/tools/quic_simple_server_stream.cc
+++ b/quic/tools/quic_simple_server_stream.cc
@@ -153,13 +153,24 @@
     return;
   }
 
-  if (!QuicContainsKey(request_headers_, ":authority") ||
-      !QuicContainsKey(request_headers_, ":path")) {
-    QUIC_DVLOG(1) << "Request headers do not contain :authority or :path.";
+  if (!QuicContainsKey(request_headers_, ":authority")) {
+    QUIC_DVLOG(1) << "Request headers do not contain :authority.";
     SendErrorResponse();
     return;
   }
 
+  if (!QuicContainsKey(request_headers_, ":path")) {
+    // CONNECT and other CONNECT-like methods (such as CONNECT-UDP) do not all
+    // require :path to be present.
+    auto it = request_headers_.find(":method");
+    if (it == request_headers_.end() ||
+        !absl::StartsWith(it->second, "CONNECT")) {
+      QUIC_DVLOG(1) << "Request headers do not contain :path.";
+      SendErrorResponse();
+      return;
+    }
+  }
+
   if (quic_simple_server_backend_ == nullptr) {
     QUIC_DVLOG(1) << "Backend is missing.";
     SendErrorResponse();
diff --git a/quic/tools/quic_simple_server_stream_test.cc b/quic/tools/quic_simple_server_stream_test.cc
index 5806ad7..541316a 100644
--- a/quic/tools/quic_simple_server_stream_test.cc
+++ b/quic/tools/quic_simple_server_stream_test.cc
@@ -77,6 +77,9 @@
   const std::string& body() const { return body_; }
   int content_length() const { return content_length_; }
   bool send_response_was_called() const { return send_response_was_called_; }
+  bool send_error_response_was_called() const {
+    return send_error_response_was_called_;
+  }
 
   absl::string_view GetHeader(absl::string_view key) const {
     auto it = request_headers_.find(key);
@@ -90,8 +93,14 @@
     QuicSimpleServerStream::SendResponse();
   }
 
+  void SendErrorResponse() override {
+    send_error_response_was_called_ = true;
+    QuicSimpleServerStream::SendErrorResponse();
+  }
+
  private:
   bool send_response_was_called_ = false;
+  bool send_error_response_was_called_ = false;
 };
 
 namespace {
@@ -778,6 +787,7 @@
   EXPECT_EQ("CONNECT-SILLY", StreamHeadersValue(":method"));
   EXPECT_EQ(body_, StreamBody());
   EXPECT_TRUE(stream_->send_response_was_called());
+  EXPECT_FALSE(stream_->send_error_response_was_called());
 }
 
 }  // namespace