diff --git a/.github/workflows/build-test.yml b/.github/workflows/build-test.yml
index 6d0764fe46..dfd31ebb80 100644
--- a/.github/workflows/build-test.yml
+++ b/.github/workflows/build-test.yml
@@ -119,12 +119,17 @@ jobs:
         run: ctest --test-dir build --output-on-failure -L badssl
 
   windows:
-    name: ${{ matrix.os }} ${{ matrix.build_type }}
+    name: ${{ matrix.os }} ${{ matrix.build_type }}${{ matrix.http == 'asio' && ' Asio without WebSockets' || '' }}
     strategy:
       fail-fast: false
       matrix:
         os: [windows-2025-vs2026, windows-2022]
         build_type: [Debug, Release]
+        http: [default]
+        include:
+          - os: windows-2025-vs2026
+            build_type: Release
+            http: asio
     runs-on: ${{ matrix.os }}
     defaults:
       run:
@@ -173,6 +178,7 @@ jobs:
         run: >-
           cmake -B build -A x64
           -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_INSTALLATION_ROOT\scripts\buildsystems\vcpkg.cmake"
+          ${{ matrix.http == 'asio' && '-DCPPREST_HTTP_CLIENT_IMPL=asio -DCPPREST_HTTP_LISTENER_IMPL=asio -DCPPREST_EXCLUDE_WEBSOCKETS=ON' || '' }}
 
       - name: Build
         run: cmake --build build --config ${{ matrix.build_type }}
diff --git a/Release/src/CMakeLists.txt b/Release/src/CMakeLists.txt
index e15aeb7fc3..52934ad2b0 100644
--- a/Release/src/CMakeLists.txt
+++ b/Release/src/CMakeLists.txt
@@ -106,7 +106,7 @@ elseif(CPPREST_PPLX_IMPL STREQUAL "linux")
   endif()
 elseif(CPPREST_PPLX_IMPL STREQUAL "win")
   target_sources(cpprest PRIVATE pplx/pplxwin.cpp)
-  if(CPPREST_WEBSOCKETS_IMPL STREQUAL "wspp")
+  if(CPPREST_WEBSOCKETS_IMPL STREQUAL "wspp" OR CPPREST_HTTP_CLIENT_IMPL STREQUAL "asio" OR CPPREST_HTTP_LISTENER_IMPL STREQUAL "asio")
     target_sources(cpprest PRIVATE pplx/threadpool.cpp ../include/pplx/threadpool.h)
     if(CPPREST_INSTALL_HEADERS)
       install(FILES ../include/pplx/threadpool.h DESTINATION include/pplx)
diff --git a/Release/src/http/listener/http_server_asio.cpp b/Release/src/http/listener/http_server_asio.cpp
index 7409864c7e..fe4549ada7 100644
--- a/Release/src/http/listener/http_server_asio.cpp
+++ b/Release/src/http/listener/http_server_asio.cpp
@@ -571,6 +571,8 @@ void asio_server_connection::shutdown()
 {
     m_close = true;
     boost::system::error_code ec;
+    // On Windows, shutdown does not complete a pending read, so cancel it
+    m_socket->cancel(ec);
     m_socket->shutdown(tcp::socket::shutdown_both, ec);
     get_request()._reply_if_not_already(status_codes::InternalError);
 }
@@ -794,9 +796,22 @@ will_deref_and_erase_t asio_server_connection::handle_headers()
         auto colon = header.find(':');
         if (colon != std::string::npos && colon != 0)
         {
-            auto name = utility::conversions::to_string_t(header.substr(0, colon));
-            auto value = utility::conversions::to_string_t(
-                header.substr(colon + 1, header.length() - (colon + 1))); // also exclude '\r'
+            utility::string_t name;
+            utility::string_t value;
+            try
+            {
+                name = utility::conversions::to_string_t(header.substr(0, colon));
+                value = utility::conversions::to_string_t(
+                    header.substr(colon + 1, header.length() - (colon + 1))); // also exclude '\r'
+            }
+            catch (const std::range_error& e) // invalid Unicode
+            {
+                currentRequest.reply(status_codes::BadRequest, e.what());
+                m_close = true;
+                (will_erase_from_parent_t) do_bad_response();
+                (will_deref_t) deref();
+                return will_deref_and_erase_t {};
+            }
             web::http::details::trim_whitespace(name);
             web::http::details::trim_whitespace(value);
 
diff --git a/Release/src/pplx/threadpool.cpp b/Release/src/pplx/threadpool.cpp
index b7602df7b3..73943ef768 100644
--- a/Release/src/pplx/threadpool.cpp
+++ b/Release/src/pplx/threadpool.cpp
@@ -4,7 +4,7 @@
  **/
 #include "stdafx.h"
 
-#if !defined(CPPREST_EXCLUDE_WEBSOCKETS) || !defined(_WIN32)
+#if !defined(_WIN32) || !defined(CPPREST_EXCLUDE_WEBSOCKETS) || defined(CPPREST_FORCE_HTTP_CLIENT_ASIO) || defined(CPPREST_FORCE_HTTP_LISTENER_ASIO)
 #include "pplx/threadpool.h"
 #include <boost/asio/detail/thread.hpp>
 #include <new>
@@ -232,4 +232,4 @@ std::unique_ptr<crossplat::threadpool> crossplat::threadpool::construct(size_t n
 {
     return std::unique_ptr<crossplat::threadpool>(new threadpool_impl(num_threads));
 }
-#endif //  !defined(CPPREST_EXCLUDE_WEBSOCKETS) || !defined(_WIN32)
+#endif //  !defined(_WIN32) || !defined(CPPREST_EXCLUDE_WEBSOCKETS) || defined(CPPREST_FORCE_HTTP_CLIENT_ASIO) || defined(CPPREST_FORCE_HTTP_LISTENER_ASIO)
diff --git a/Release/tests/functional/http/client/authentication_tests.cpp b/Release/tests/functional/http/client/authentication_tests.cpp
index f75e8ab60e..c90046be37 100644
--- a/Release/tests/functional/http/client/authentication_tests.cpp
+++ b/Release/tests/functional/http/client/authentication_tests.cpp
@@ -58,7 +58,7 @@ namespace client
 {
 SUITE(authentication_tests)
 {
-    TEST_FIXTURE(uri_address, auth_no_data, "Ignore:Linux", "89", "Ignore:Apple", "89")
+    TEST_FIXTURE(uri_address, auth_no_data, IGNORE_IF_HTTP_CLIENT_ASIO, "89")
     {
         pplx::task<void> t, t2;
         {
@@ -115,7 +115,7 @@ SUITE(authentication_tests)
 
 // TFS 648783
 #ifndef __cplusplus_winrt
-    TEST_FIXTURE(uri_address, proxy_auth_known_contentlength, "Ignore:Linux", "88", "Ignore:Apple", "88")
+    TEST_FIXTURE(uri_address, proxy_auth_known_contentlength, IGNORE_IF_HTTP_CLIENT_ASIO, "88")
     {
         pplx::task<void> t, t2;
         {
@@ -169,7 +169,7 @@ SUITE(authentication_tests)
     }
 #endif
 
-    TEST_FIXTURE(uri_address, proxy_auth_noseek, "Ignore:Linux", "88", "Ignore:Apple", "88")
+    TEST_FIXTURE(uri_address, proxy_auth_noseek, IGNORE_IF_HTTP_CLIENT_ASIO, "88")
     {
         web::http::uri uri(U("http://localhost:24567/"));
         test_http_server::scoped_server scoped(uri);
@@ -200,7 +200,7 @@ SUITE(authentication_tests)
 
 // Must specify content length with winrt client, so this test case isn't possible.
 #ifndef __cplusplus_winrt
-    TEST_FIXTURE(uri_address, proxy_auth_unknown_contentlength, "Ignore:Linux", "88", "Ignore:Apple", "88")
+    TEST_FIXTURE(uri_address, proxy_auth_unknown_contentlength, IGNORE_IF_HTTP_CLIENT_ASIO, "88")
     {
         pplx::task<void> t;
         {
@@ -275,7 +275,7 @@ SUITE(authentication_tests)
     // Fails on WinRT due to TFS 648278
     // Accessing a server that supports auth, but returns 401, even after the user has provided valid creds
     // We're making sure the error is reported properly, and the response data from the second response is received
-    TEST_FIXTURE(uri_address, error_after_valid_credentials, "Ignore:Linux", "89", "Ignore:Apple", "89")
+    TEST_FIXTURE(uri_address, error_after_valid_credentials, IGNORE_IF_HTTP_CLIENT_ASIO, "89")
     {
         pplx::task<void> t;
         {
@@ -477,7 +477,7 @@ SUITE(authentication_tests)
     }
 #endif // __cplusplus_winrt
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(CPPREST_FORCE_HTTP_CLIENT_ASIO)
 #if !defined(__cplusplus_winrt)
     TEST_FIXTURE(server_properties, set_user_options, "Requires", "Server;UserName;Password")
     {
@@ -633,7 +633,7 @@ SUITE(authentication_tests)
         http_client client(m_uri, config);
         VERIFY_THROWS(client.request(methods::GET).get(), std::runtime_error);
     }
-#endif // _WIN32
+#endif // defined(_WIN32) && !defined(CPPREST_FORCE_HTTP_CLIENT_ASIO)
 
     // Fix for 522831 AV after failed authentication attempt
     // apis.live.net now returns 400 Bad Request instead of 401 Unauthorized
diff --git a/Release/tests/functional/http/listener/connections_and_errors.cpp b/Release/tests/functional/http/listener/connections_and_errors.cpp
index 87f4a7cee6..802010b8a3 100644
--- a/Release/tests/functional/http/listener/connections_and_errors.cpp
+++ b/Release/tests/functional/http/listener/connections_and_errors.cpp
@@ -310,7 +310,7 @@ SUITE(connections_and_errors)
         VERIFY_THROWS(listener.open().wait(), http_exception);
     }
 
-    TEST_FIXTURE(uri_address, try_port_already_in_use, "Ignore:Linux", "Bug 879077", "Ignore:Apple", "Bug 879077")
+    TEST_FIXTURE(uri_address, try_port_already_in_use, IGNORE_IF_HTTP_LISTENER_ASIO, "Bug 879077")
     {
         test_http_server::scoped_server scoped(m_uri);
         http_listener listener(m_uri);
@@ -450,12 +450,7 @@ SUITE(connections_and_errors)
         return errorCode;
     }
 
-    TEST_FIXTURE(uri_address,
-                 request_content_ready_timeout,
-                 "Ignore:Linux",
-                 "Unsuitable until 813276",
-                 "Ignore:Apple",
-                 "Unsuitable until 813276")
+    TEST_FIXTURE(uri_address, request_content_ready_timeout, IGNORE_IF_HTTP_LISTENER_ASIO, "Unsuitable until 813276")
     {
 #if !defined(_WIN32) || defined(CPPREST_FORCE_HTTP_LISTENER_ASIO)
         throw std::runtime_error(
diff --git a/Release/tests/functional/http/utilities/include/http_test_utilities.h b/Release/tests/functional/http/utilities/include/http_test_utilities.h
index 2f66e56a88..36428f3f0d 100644
--- a/Release/tests/functional/http/utilities/include/http_test_utilities.h
+++ b/Release/tests/functional/http/utilities/include/http_test_utilities.h
@@ -16,3 +16,16 @@
 #include "test_http_client.h"
 #include "test_http_server.h"
 #include "test_server_utilities.h"
+
+// Test properties that ignore a test when the library uses the Asio HTTP client or listener, on any platform.
+// The test runner cannot tell which implementations the library uses.
+#if defined(CPPREST_FORCE_HTTP_CLIENT_ASIO)
+#define IGNORE_IF_HTTP_CLIENT_ASIO "Ignore"
+#else
+#define IGNORE_IF_HTTP_CLIENT_ASIO "Ignore:None"
+#endif
+#if defined(CPPREST_FORCE_HTTP_LISTENER_ASIO)
+#define IGNORE_IF_HTTP_LISTENER_ASIO "Ignore"
+#else
+#define IGNORE_IF_HTTP_LISTENER_ASIO "Ignore:None"
+#endif