diff --git a/.github/actions/setup-llvm-mingw/action.yml b/.github/actions/setup-llvm-mingw/action.yml
index 04942cce4..9926bbe93 100644
--- a/.github/actions/setup-llvm-mingw/action.yml
+++ b/.github/actions/setup-llvm-mingw/action.yml
@@ -12,19 +12,20 @@ inputs:
 outputs:
   llvm-path:
     description: "The path in which llvm-mingw is installed to"
-    value: ${{ steps.setup-llvm.outputs.llvm-path }}
+    value: ${{ ((runner.os == 'Windows') && steps.setup-llvm.outputs.llvm-path) || steps.setup-llvm-linux.outputs.llvm-path }}
 runs:
   using: "composite"
   steps:
-    - name: Cache llvm-mingw
+    - name: Cache llvm-mingw (Windows)
       id: cache-llvm
+      if: runner.os == 'Windows'
       uses: actions/cache@v3
       with:
         path: .llvm-mingw
         key: llvm-mingw-${{ runner.os }}-${{ inputs.llvm-mingw-version }}-${{ inputs.host-arch }}
 
-    - name: Install llvm-mingw ${{ inputs.llvm-mingw-version }} (${{ inputs.host-arch }})
-      if: steps.cache-llvm.outputs.cache-hit != 'true'
+    - name: Install llvm-mingw ${{ inputs.llvm-mingw-version }} (Windows ${{ inputs.host-arch }})
+      if: runner.os == 'Windows' && steps.cache-llvm.outputs.cache-hit != 'true'
       shell: pwsh
       run: |
         $llvm_mingw_version = "${{ inputs.llvm-mingw-version }}"
@@ -33,8 +34,9 @@ runs:
         7z x llvm-mingw.zip -o"$pwd\.llvm-mingw"
         rm llvm-mingw.zip
 
-    - name: Set up llvm-mingw
+    - name: Set up llvm-mingw (Windows)
       id: setup-llvm
+      if: runner.os == 'Windows'
       shell: pwsh
       run: |
         $llvm_mingw_version = "${{ inputs.llvm-mingw-version }}"
@@ -44,3 +46,34 @@ runs:
         Add-Content $env:GITHUB_PATH "$pwd\.llvm-mingw\llvm-mingw-${llvm_mingw_version}-ucrt-${llvm_arch}\bin"
         # for the ASAN runtime DLL:
         Add-Content $env:GITHUB_PATH "$pwd\.llvm-mingw\llvm-mingw-${llvm_mingw_version}-ucrt-${llvm_arch}\${llvm_arch}-w64-mingw32\bin"
+
+    - name: Cache llvm-mingw (Linux)
+      id: cache-llvm-linux
+      if: runner.os == 'Linux'
+      uses: actions/cache@v3
+      with:
+        path: /opt/llvm-mingw
+        key: llvm-mingw-${{ runner.os }}-${{ inputs.llvm-mingw-version }}-${{ inputs.host-arch }}
+
+    - name: Install llvm-mingw ${{ inputs.llvm-mingw-version }} (Linux ${{ inputs.host-arch }})
+      if: runner.os == 'Linux' && steps.cache-llvm-linux.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        llvm_mingw_version="${{ inputs.llvm-mingw-version }}"
+        llvm_arch="${{ inputs.host-arch }}"
+        mkdir -p /opt/llvm-mingw
+        cd /opt/llvm-mingw
+        curl -L https://github.com/mstorsjo/llvm-mingw/releases/download/20220906/llvm-mingw-${llvm_mingw_version}-ucrt-ubuntu-18.04-${llvm_arch}.tar.xz | tar xJ --strip-components=1
+
+    - name: Set up llvm-mingw (Linux)
+      id: setup-llvm-linux
+      if: runner.os == 'Linux'
+      shell: bash
+      run: |
+        cd /opt/llvm-mingw
+        if [ ! -x bin/clang++ ]; then
+          echo "$PWD/bin/clang++ not found or not executable!"
+          exit 1
+        fi
+        echo "llvm-path=$PWD/llvm-mingw" >> $GITHUB_OUTPUT
+        echo "$PWD/bin" >> $GITHUB_PATH
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 36de522bf..dca6c31bc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -252,6 +252,7 @@ jobs:
   test-llvm-mingw-cppwinrt:
     name: 'llvm-mingw: Build and test'
     strategy:
+      fail-fast: false
       matrix:
         arch: [i686, x86_64]
         config: [Debug, Release]
@@ -262,6 +263,8 @@ jobs:
       - id: setup-llvm
         name: Set up llvm-mingw
         uses: ./.github/actions/setup-llvm-mingw
+        with:
+          host-arch: ${{ matrix.arch }}
 
       - name: Build cppwinrt
         run: |
@@ -335,19 +338,117 @@ jobs:
     name: 'cross: Test run on Windows'
     needs: build-linux-cross-cppwinrt
     strategy:
+      fail-fast: false
       matrix:
         arch: [i686, x86_64]
     runs-on: windows-latest
     steps:
+      - uses: actions/checkout@v3
+
       - name: Fetch cppwinrt executable
         uses: actions/download-artifact@v3
         with:
           name: cross-build-${{ matrix.arch }}-bin
-          path: ./
+          path: ./.test
 
       - name: Run cppwinrt to build projection
         run: |
-          .\cppwinrt.exe -in local -out .\ -verbose
+          .\.test\cppwinrt.exe -in local -out .\.test\out -verbose
+
+      - id: setup-llvm
+        name: Set up llvm-mingw
+        uses: ./.github/actions/setup-llvm-mingw
+        with:
+          host-arch: ${{ matrix.arch }}
+
+      - name: Build cppwinrt tests
+        run: |
+          mkdir build
+          cd build
+          cmake ../test -G"MinGW Makefiles" -DCMAKE_BUILD_TYPE=Debug `
+            -DCPPWINRT_PROJECTION_INCLUDE_DIR="../.test/out" `
+            -DDOWNLOAD_WINDOWSNUMERICS=TRUE
+          cmake --build . -j2
+
+      - name: Run tests
+        run: |
+          cd build
+          ctest --verbose
+
+  build-linux-native-cppwinrt:
+    name: 'linux: GCC native build + llvm-mingw cross-build tests'
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Build cppwinrt
+        run: |
+          cmake -S . -B build/native/ \
+            -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+            -DCMAKE_INSTALL_PREFIX=$PWD/install/
+          cmake --build build/native/ --target install -j2
+
+      - name: Test run (cppwinrt -?)
+        run: |
+          install/bin/cppwinrt -?
+
+      - name: Test run (build projection using Windows.winmd)
+        run: |
+          curl -o Windows.winmd -L https://github.com/microsoft/windows-rs/raw/master/crates/libs/metadata/default/Windows.winmd
+          install/bin/cppwinrt -in Windows.winmd -out /tmp/cppwinrt -verbose
+
+      - id: setup-llvm
+        name: Set up llvm-mingw
+        uses: ./.github/actions/setup-llvm-mingw
+
+      - name: Cross-build tests using projection
+        run: |
+          cmake -S test -B build/cross-tests --toolchain "$PWD/cross-mingw-toolchain.cmake" \
+            -DCMAKE_SYSTEM_PROCESSOR=x86_64 \
+            -DCMAKE_BUILD_TYPE=Debug \
+            -DCMAKE_CXX_FLAGS="-static" \
+            -DCPPWINRT_PROJECTION_INCLUDE_DIR=/tmp/cppwinrt \
+            -DDOWNLOAD_WINDOWSNUMERICS=TRUE
+          cmake --build build/cross-tests -j2
+
+      - name: Upload built tests
+        uses: actions/upload-artifact@v3
+        with:
+          name: linux-native-cppwinrt-cross-build-tests-x86_64-bin
+          path: build/cross-tests/*.exe
+
+  test-linux-native-cppwinrt-cross-tests:
+    name: 'linux: Run llvm-mingw cross-build tests'
+    needs: build-linux-native-cppwinrt
+    strategy:
+      matrix:
+        arch: [x86_64]
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Fetch test executables
+        uses: actions/download-artifact@v3
+        with:
+          name: linux-native-cppwinrt-cross-build-tests-${{ matrix.arch }}-bin
+          path: ./
+
+      - name: Run tests
+        run: |
+          $test_exes = ls *.exe -Name
+          $has_failed_tests = 0
+          foreach ($test_exe in $test_exes) {
+            echo "::group::Run '$test_exe'"
+            & .\$test_exe
+            echo "::endgroup::"
+            if ($LastExitCode -ne 0) {
+              echo "::error::Test '$test_exe' failed!"
+              $has_failed_tests = 1
+            }
+          }
+          if ($has_failed_tests -ne 0) {
+            exit 1
+          }
 
   build-msvc-natvis:
     name: 'Build natvis'
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b983c4587..e8ef5fa4a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,9 @@
 # This CMake build file is intended for use with the llvm-mingw toolchain:
 # https://github.com/mstorsjo/llvm-mingw
 #
+# It also works for building natively on Linux, or cross-building from Linux
+# for running on Windows with a mingw-w64 toolchain.
+#
 # It most probably doesn't work with MSVC.
 
 cmake_minimum_required(VERSION 3.16)
@@ -16,8 +19,10 @@ if(CPPWINRT_BUILD_VERSION STREQUAL "2.3.4.5" OR CPPWINRT_BUILD_VERSION STREQUAL
 endif()
 message(STATUS "Using version string: ${CPPWINRT_BUILD_VERSION}")
 
-# WinMD uses CreateFile2 which requires Windows 8.
-add_compile_definitions(_WIN32_WINNT=0x0602)
+if(WIN32)
+    # WinMD uses CreateFile2 which requires Windows 8.
+    add_compile_definitions(_WIN32_WINNT=0x0602)
+endif()
 
 
 # === prebuild: Generator tool for strings.cpp, strings.h, version.rc ===
@@ -77,32 +82,37 @@ set(CPPWINRT_HEADERS
     cppwinrt/type_writers.h
 )
 
-add_custom_command(
-    OUTPUT
-        "${PROJECT_BINARY_DIR}/app.manifest"
-    COMMAND ${CMAKE_COMMAND} -E copy "${PROJECT_SOURCE_DIR}/cppwinrt/app.manifest" "${PROJECT_BINARY_DIR}/app.manifest"
-    DEPENDS "${PROJECT_SOURCE_DIR}/cppwinrt/app.manifest"
-    VERBATIM
-)
-# Do the configure_file dance so that app.manifest.rc don't get modified every
-# single time the project is reconfigured and trigger a rebuild.
-file(WRITE "${PROJECT_BINARY_DIR}/app.manifest.rc.in" "1 24 \"app.manifest\"\n")
-configure_file(
-    "${PROJECT_BINARY_DIR}/app.manifest.rc.in"
-    "${PROJECT_BINARY_DIR}/app.manifest.rc"
-    COPYONLY
-)
+if(WIN32)
+    add_custom_command(
+        OUTPUT
+            "${PROJECT_BINARY_DIR}/app.manifest"
+        COMMAND ${CMAKE_COMMAND} -E copy "${PROJECT_SOURCE_DIR}/cppwinrt/app.manifest" "${PROJECT_BINARY_DIR}/app.manifest"
+        DEPENDS "${PROJECT_SOURCE_DIR}/cppwinrt/app.manifest"
+        VERBATIM
+    )
+    # Do the configure_file dance so that app.manifest.rc don't get modified every
+    # single time the project is reconfigured and trigger a rebuild.
+    file(WRITE "${PROJECT_BINARY_DIR}/app.manifest.rc.in" "1 24 \"app.manifest\"\n")
+    configure_file(
+        "${PROJECT_BINARY_DIR}/app.manifest.rc.in"
+        "${PROJECT_BINARY_DIR}/app.manifest.rc"
+        COPYONLY
+    )
 
-set(CPPWINRT_RESOURCES
-    "${PROJECT_BINARY_DIR}/app.manifest"
-    "${PROJECT_BINARY_DIR}/app.manifest.rc"
-    "${PROJECT_BINARY_DIR}/version.rc"
-)
+    set(CPPWINRT_RESOURCES
+        "${PROJECT_BINARY_DIR}/app.manifest"
+        "${PROJECT_BINARY_DIR}/app.manifest.rc"
+        "${PROJECT_BINARY_DIR}/version.rc"
+    )
+endif()
 
 add_executable(cppwinrt ${CPPWINRT_SRCS} ${CPPWINRT_RESOURCES} ${CPPWINRT_HEADERS})
 target_compile_definitions(cppwinrt PRIVATE CPPWINRT_VERSION_STRING="${CPPWINRT_BUILD_VERSION}")
 target_include_directories(cppwinrt PRIVATE ${PROJECT_BINARY_DIR})
-target_link_libraries(cppwinrt shlwapi)
+
+if(WIN32)
+    target_link_libraries(cppwinrt shlwapi)
+endif()
 
 install(TARGETS cppwinrt)
 
@@ -158,15 +168,17 @@ int main() {}
         add_dependencies(cppwinrt gen-libxmllite)
     endif()
 endif()
-target_link_libraries(cppwinrt "${XMLLITE_LIBRARY}")
+if(WIN32)
+    target_link_libraries(cppwinrt "${XMLLITE_LIBRARY}")
+endif()
 
 
 # === winmd: External header-only library for reading winmd files ===
 
 include(ExternalProject)
 ExternalProject_Add(winmd
-    URL https://github.com/microsoft/winmd/releases/download/1.0.210629.2/Microsoft.Windows.WinMD.1.0.210629.2.nupkg
-    URL_HASH SHA256=4c5f29d948f5b3d724d229664c8f8e4823250d3c9f23ad8067b732fc7076d8c7
+    GIT_REPOSITORY https://github.com/microsoft/winmd.git
+    GIT_TAG 0f1eae3bfa63fa2ba3c2912cbfe72a01db94cc5a
     CONFIGURE_COMMAND ""
     BUILD_COMMAND ""
     INSTALL_COMMAND ""
@@ -174,10 +186,10 @@ ExternalProject_Add(winmd
 add_dependencies(cppwinrt winmd)
 ExternalProject_Get_Property(winmd SOURCE_DIR)
 set(winmd_SOURCE_DIR "${SOURCE_DIR}")
-target_include_directories(cppwinrt PRIVATE "${winmd_SOURCE_DIR}")
+target_include_directories(cppwinrt PRIVATE "${winmd_SOURCE_DIR}/src")
 
 
-if(NOT CMAKE_CROSSCOMPILING)
+if(WIN32 AND NOT CMAKE_CROSSCOMPILING)
     include(CTest)
     if(BUILD_TESTING)
         add_subdirectory(test)
diff --git a/cppwinrt/cmd_reader.h b/cppwinrt/cmd_reader.h
index bb5454258..7faf49e4f 100644
--- a/cppwinrt/cmd_reader.h
+++ b/cppwinrt/cmd_reader.h
@@ -3,6 +3,7 @@
 #include <cassert>
 #include <array>
 #include <limits>
+#include <climits>
 #include <cstdint>
 #include <string>
 #include <string_view>
@@ -12,12 +13,16 @@
 #include <filesystem>
 #include <fstream>
 #include <regex>
+
+#if defined(_WIN32) || defined(_WIN64)
 #include <windows.h>
 #include <shlwapi.h>
 #include <xmllite.h>
+#endif
 
 namespace cppwinrt
 {
+#if defined(_WIN32) || defined(_WIN64)
     struct registry_key
     {
         HKEY handle{};
@@ -291,6 +296,7 @@ namespace cppwinrt
 
         return result;
     }
+#endif /* defined(_WIN32) || defined(_WIN64) */
 
     [[noreturn]] inline void throw_invalid(std::string const& message)
     {
@@ -440,6 +446,7 @@ namespace cppwinrt
                 }
                 if (path == "local")
                 {
+#if defined(_WIN32) || defined(_WIN64)
                     std::array<char, 260> local{};
 #ifdef _WIN64
                     ExpandEnvironmentStringsA("%windir%\\System32\\WinMetadata", local.data(), static_cast<uint32_t>(local.size()));
@@ -447,6 +454,9 @@ namespace cppwinrt
                     ExpandEnvironmentStringsA("%windir%\\SysNative\\WinMetadata", local.data(), static_cast<uint32_t>(local.size()));
 #endif
                     add_directory(local.data());
+#else /* defined(_WIN32) || defined(_WIN64) */
+                    throw_invalid("Spec '", path, "' not supported outside of Windows");
+#endif /* defined(_WIN32) || defined(_WIN64) */
                     continue;
                 }
 
@@ -454,7 +464,11 @@ namespace cppwinrt
 
                 if (path == "sdk" || path == "sdk+")
                 {
+#if defined(_WIN32) || defined(_WIN64)
                     sdk_version = get_sdk_version();
+#else /* defined(_WIN32) || defined(_WIN64) */
+                    throw_invalid("Spec '", path, "' not supported outside of Windows");
+#endif /* defined(_WIN32) || defined(_WIN64) */
                 }
                 else
                 {
@@ -469,6 +483,7 @@ namespace cppwinrt
 
                 if (!sdk_version.empty())
                 {
+#if defined(_WIN32) || defined(_WIN64)
                     auto sdk_path = get_sdk_path();
                     auto xml_path = sdk_path;
                     xml_path /= L"Platforms\\UAP";
@@ -490,6 +505,9 @@ namespace cppwinrt
                         // Not all Extension SDKs include an SDKManifest.xml file; ignore those which do not (e.g. WindowsIoT).
                         add_files_from_xml(files, sdk_version, xml_path, sdk_path, xml_requirement::optional);
                     }
+#else /* defined(_WIN32) || defined(_WIN64) */
+                    throw_invalid("Spec '", path, "' not supported outside of Windows");
+#endif /* defined(_WIN32) || defined(_WIN64) */
 
                     continue;
                 }
@@ -531,7 +549,11 @@ namespace cppwinrt
         template<typename O, typename L>
         void extract_option(std::string_view arg, O const& options, L& last)
         {
-            if (arg[0] == '-' || arg[0] == '/')
+            if (arg[0] == '-'
+#if defined(_WIN32) || defined(_WIN64)
+                || arg[0] == '/'
+#endif
+            )
             {
                 arg.remove_prefix(1);
                 last = find(options, arg);
diff --git a/cppwinrt/main.cpp b/cppwinrt/main.cpp
index 5834d868f..16700a863 100644
--- a/cppwinrt/main.cpp
+++ b/cppwinrt/main.cpp
@@ -70,10 +70,14 @@ Copyright (c) Microsoft Corporation. All rights reserved.
 Where <spec> is one or more of:
 
   path                Path to winmd file or recursively scanned folder
-  local               Local ^%WinDir^%\System32\WinMetadata folder
+)"
+#if defined(_WIN32) || defined(_WIN64)
+R"(  local               Local ^%WinDir^%\System32\WinMetadata folder
   sdk[+]              Current version of Windows SDK [with extensions]
   10.0.12345.0[+]     Specific version of Windows SDK [with extensions]
-)";
+)"
+#endif
+        ;
         w.write(format, CPPWINRT_VERSION_STRING, bind_each(printOption, options));
     }
 
@@ -94,7 +98,7 @@ Where <spec> is one or more of:
         path output_folder = args.value("output", ".");
         create_directories(output_folder / "winrt/impl");
         settings.output_folder = canonical(output_folder).string();
-        settings.output_folder += '\\';
+        settings.output_folder += std::filesystem::path::preferred_separator;
 
         for (auto && include : args.values("include"))
         {
@@ -146,7 +150,7 @@ Where <spec> is one or more of:
             {
                 create_directories(component);
                 settings.component_folder = canonical(component).string();
-                settings.component_folder += '\\';
+                settings.component_folder += std::filesystem::path::preferred_separator;
             }
         }
     }
@@ -270,6 +274,7 @@ Where <spec> is one or more of:
             {
                 {
                     char* path = argv[0];
+#if defined(_WIN32) || defined(_WIN64)
                     char path_buf[32768];
                     DWORD path_size = GetModuleFileNameA(nullptr, path_buf, sizeof(path_buf));
                     if (path_size)
@@ -277,6 +282,7 @@ Where <spec> is one or more of:
                         path_buf[sizeof(path_buf) - 1] = 0;
                         path = path_buf;
                     }
+#endif
                     w.write(" tool:  %\n", path);
                 }
                 w.write(" ver:   %\n", CPPWINRT_VERSION_STRING);
diff --git a/cppwinrt/text_writer.h b/cppwinrt/text_writer.h
index 3e210db83..ee723c703 100644
--- a/cppwinrt/text_writer.h
+++ b/cppwinrt/text_writer.h
@@ -128,7 +128,16 @@ namespace cppwinrt
         void write_printf(char const* format, Args const&... args)
         {
             char buffer[128];
+#if defined(_WIN32) || defined(_WIN64)
             size_t const size = sprintf_s(buffer, format, args...);
+#else
+            size_t size = snprintf(buffer, sizeof(buffer), format, args...);
+            if (size > sizeof(buffer) - 1)
+            {
+                fprintf(stderr, "\n*** WARNING: writer_base::write_printf -- buffer too small\n");
+                size = sizeof(buffer) - 1;
+            }
+#endif
             write(std::string_view{ buffer, size });
         }
 
diff --git a/prebuild/main.cpp b/prebuild/main.cpp
index 52a750776..3e427d32b 100644
--- a/prebuild/main.cpp
+++ b/prebuild/main.cpp
@@ -19,9 +19,11 @@ int main(int const argc, char** argv)
     strings_h.write(R"(
 #pragma once
 namespace cppwinrt::strings {
+extern "C++" {
 )");
 
     strings_cpp.write(R"(
+#include "strings.h"
 namespace cppwinrt::strings {
 )");
 
@@ -41,7 +43,7 @@ namespace cppwinrt::strings {
         strings_h.write(R"(extern char const %[%];
 )",
             name.string(),
-            static_cast<uint64_t>(view.size()));
+            static_cast<uint64_t>(view.size() + 1));
 
         strings_cpp.write(R"(extern char const %[] = R"xyz()xyz"
 )",
@@ -66,6 +68,7 @@ namespace cppwinrt::strings {
 
     strings_h.write(R"(
 }
+}
 )");
 
     strings_cpp.write(R"(
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 19ce748a7..6cf1aa3ca 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -1,11 +1,23 @@
+cmake_minimum_required(VERSION 3.16)
+
+if(NOT DEFINED PROJECT_NAME)
+    project(cppwinrt-tests)
+    set(STANDALONE_TESTING 1)
+    include(CTest)
+    if(NOT BUILD_TESTING)
+        message(NOTICE "BUILD_TESTING is OFF, nothing to do.")
+        return()
+    endif()
+endif()
+
 # The tests use newer C++ features.
 set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED True)
 
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
 
 include_directories("${CMAKE_CURRENT_SOURCE_DIR}")
-include_directories("${PROJECT_SOURCE_DIR}/cppwinrt")
-include_directories("${CMAKE_CURRENT_BINARY_DIR}/cppwinrt")
+include_directories("${CMAKE_CURRENT_SOURCE_DIR}/../cppwinrt")
 
 function(TestIsX64 OUTPUT_VARNAME)
     include(CheckCXXSourceCompiles)
@@ -51,18 +63,28 @@ if(NOT HAS_WINDOWSNUMERICS AND DOWNLOAD_WINDOWSNUMERICS)
 endif()
 
 
-add_custom_command(
-    OUTPUT
-        "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt/winrt/base.h"
-    COMMAND "${PROJECT_BINARY_DIR}/cppwinrt" -input local -output "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt" -verbose
-    DEPENDS
-        cppwinrt
-    VERBATIM
-)
-add_custom_target(build-cppwinrt-projection
-    DEPENDS
-        "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt/winrt/base.h"
-)
+if(STANDALONE_TESTING)
+    add_custom_target(build-cppwinrt-projection)
+    set(CPPWINRT_PROJECTION_INCLUDE_DIR "" CACHE PATH "Include path for the C++/WinRT projection headers")
+    if(NOT CPPWINRT_PROJECTION_INCLUDE_DIR)
+        message(FATAL_ERROR "CPPWINRT_PROJECTION_INCLUDE_DIR is not specified.")
+    endif()
+else()
+    set(CPPWINRT_PROJECTION_INCLUDE_DIR "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt")
+    add_custom_command(
+        OUTPUT
+            "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt/winrt/base.h"
+        COMMAND cppwinrt -input local -output "${CPPWINRT_PROJECTION_INCLUDE_DIR}" -verbose
+        DEPENDS
+            cppwinrt
+        VERBATIM
+    )
+    add_custom_target(build-cppwinrt-projection
+        DEPENDS
+            "${CMAKE_CURRENT_BINARY_DIR}/cppwinrt/winrt/base.h"
+    )
+endif()
+include_directories("${CPPWINRT_PROJECTION_INCLUDE_DIR}")
 
 
 set(ENABLE_TEST_SANITIZERS FALSE CACHE BOOL "Enable ASan and UBSan for the tests.")
diff --git a/test/old_tests/UnitTests/Hash.cpp b/test/old_tests/UnitTests/Hash.cpp
index 756beacab..7464da6ab 100644
--- a/test/old_tests/UnitTests/Hash.cpp
+++ b/test/old_tests/UnitTests/Hash.cpp
@@ -1,5 +1,5 @@
 #include "pch.h"
-#include "winrt\Windows.Foundation.h"
+#include "winrt/Windows.Foundation.h"
 #include "catch.hpp"
 #include <unordered_set>
 #include <set>
diff --git a/test/old_tests/UnitTests/pch.h b/test/old_tests/UnitTests/pch.h
index 26990fd1c..4b940b552 100644
--- a/test/old_tests/UnitTests/pch.h
+++ b/test/old_tests/UnitTests/pch.h
@@ -10,29 +10,29 @@
 #include <unknwn.h>
 #undef GetCurrentTime
 
-#include "winrt\Windows.Foundation.Collections.h"
-#include "winrt\Windows.Foundation.Diagnostics.h"
-#include "winrt\Windows.ApplicationModel.Activation.h"
-#include "winrt\Windows.ApplicationModel.Core.h"
-#include "winrt\Windows.ApplicationModel.DataTransfer.h"
-#include "winrt\Windows.ApplicationModel.Store.h"
-#include "winrt\Windows.Data.Json.h"
-#include "winrt\Windows.Devices.Perception.Provider.h"
-#include "winrt\Windows.Devices.Sms.h"
-#include "winrt\Windows.Graphics.Display.h"
-#include "winrt\Windows.Graphics.Effects.h"
-#include "winrt\Windows.Management.Deployment.h"
-#include "winrt\Windows.Media.Audio.h"
-#include "winrt\Windows.Media.Core.h"
-#include "winrt\Windows.Media.Transcoding.h"
-#include "winrt\Windows.Networking.Sockets.h"
-#include "winrt\Windows.Security.Cryptography.Certificates.h"
-#include "winrt\Windows.Storage.Streams.h"
-#include "winrt\Windows.System.Threading.h"
-#include "winrt\Windows.UI.Core.h"
-#include "winrt\Windows.UI.Composition.h"
-#include "winrt\Windows.UI.Xaml.Controls.h"
-#include "winrt\Windows.UI.Xaml.Interop.h"
-#include "winrt\Windows.Web.AtomPub.h"
-#include "winrt\Windows.Web.Http.Headers.h"
-#include "winrt\Windows.Web.Syndication.h"
+#include "winrt/Windows.Foundation.Collections.h"
+#include "winrt/Windows.Foundation.Diagnostics.h"
+#include "winrt/Windows.ApplicationModel.Activation.h"
+#include "winrt/Windows.ApplicationModel.Core.h"
+#include "winrt/Windows.ApplicationModel.DataTransfer.h"
+#include "winrt/Windows.ApplicationModel.Store.h"
+#include "winrt/Windows.Data.Json.h"
+#include "winrt/Windows.Devices.Perception.Provider.h"
+#include "winrt/Windows.Devices.Sms.h"
+#include "winrt/Windows.Graphics.Display.h"
+#include "winrt/Windows.Graphics.Effects.h"
+#include "winrt/Windows.Management.Deployment.h"
+#include "winrt/Windows.Media.Audio.h"
+#include "winrt/Windows.Media.Core.h"
+#include "winrt/Windows.Media.Transcoding.h"
+#include "winrt/Windows.Networking.Sockets.h"
+#include "winrt/Windows.Security.Cryptography.Certificates.h"
+#include "winrt/Windows.Storage.Streams.h"
+#include "winrt/Windows.System.Threading.h"
+#include "winrt/Windows.UI.Core.h"
+#include "winrt/Windows.UI.Composition.h"
+#include "winrt/Windows.UI.Xaml.Controls.h"
+#include "winrt/Windows.UI.Xaml.Interop.h"
+#include "winrt/Windows.Web.AtomPub.h"
+#include "winrt/Windows.Web.Http.Headers.h"
+#include "winrt/Windows.Web.Syndication.h"
diff --git a/test/test/guid_include.cpp b/test/test/guid_include.cpp
index 07a7d4988..212b6b0e5 100644
--- a/test/test/guid_include.cpp
+++ b/test/test/guid_include.cpp
@@ -1,3 +1,3 @@
 #include "winrt/base.h"
-#include <Unknwn.h>
+#include <unknwn.h>
 #include "winrt/Windows.Foundation.h"
diff --git a/test/test_fast_fwd/FastForwarderTests.cpp b/test/test_fast_fwd/FastForwarderTests.cpp
index 5a10216bf..8a80eaf1c 100644
--- a/test/test_fast_fwd/FastForwarderTests.cpp
+++ b/test/test_fast_fwd/FastForwarderTests.cpp
@@ -1,8 +1,8 @@
 #include "pch.h"
 #include <string_view>
-#include "winrt\fast_forward.h"
-#include "winrt\Windows.Foundation.h"
-#include "winrt\FastForwarderTest.h"
+#include "winrt/fast_forward.h"
+#include "winrt/Windows.Foundation.h"
+#include "winrt/FastForwarderTest.h"
 #include "Class.g.h"
 
 using namespace std::literals;