diff --git a/.github/workflows/CI-cygwin.yml b/.github/workflows/CI-cygwin.yml
new file mode 100644
index 00000000..a3de616d
--- /dev/null
+++ b/.github/workflows/CI-cygwin.yml
@@ -0,0 +1,89 @@
+name: CI-cygwin
+
+on: [push, pull_request]
+
+permissions:
+  contents: read
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build:
+
+    strategy:
+      matrix:
+        compiler: [g++]
+      fail-fast: false
+
+    runs-on: windows-2025
+
+    env:
+      CXX: ${{ matrix.compiler }}
+
+    steps:
+      - run: |
+          git config --global core.autocrlf input
+
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+
+      - name: Set up Cygwin
+        uses: cygwin/cygwin-install-action@v6
+        with:
+          platform: 'x86_64'
+          packages: |
+            gcc-g++
+            python3
+            cmake
+
+      - name: make simplecpp
+        shell: cmd
+        run: |
+          pwd
+          ls -l
+          make -j1 CXXOPTS="-Werror"
+
+      - name: make simplecpp
+        run: |
+          pwd
+          ls -l
+          make -j1 CXXOPTS="-Werror"
+
+      - name: run test
+        run: |
+          make -j1 test
+
+      - name: selfcheck
+        run: |
+          make -j1 selfcheck
+
+      - name: Run CMake
+        run: |
+          cmake -S . -B cmake.output -DCMAKE_COMPILE_WARNING_AS_ERROR=On
+
+      - name: CMake simplecpp
+        run: |
+          cmake --build cmake.output --target simplecpp -- -j 4
+
+      - name: CMake testrunner
+        run: |
+          cmake --build cmake.output --target testrunner -- -j 4
+
+      - name: Run testrunner
+        run: |
+          ./cmake.output/testrunner
+
+      - name: Run with libstdc++ debug mode
+        if: matrix.compiler == 'g++'
+        run: |
+          make clean
+          make -j1 test selfcheck CXXOPTS="-Werror -g3 -D_GLIBCXX_DEBUG"
+
+      - name: Run with libc++ hardening mode
+        if: matrix.compiler == 'clang++' && matrix.msystem == 'CLANG64'
+        run: |
+          make clean
+          make -j1 test selfcheck CXXOPTS="-Werror -stdlib=libc++ -g3 -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG" LDOPTS="-lc++"
diff --git a/.github/workflows/CI-unixish.yml b/.github/workflows/CI-unixish.yml
deleted file mode 100644
index b4089ee1..00000000
--- a/.github/workflows/CI-unixish.yml
+++ /dev/null
@@ -1,163 +0,0 @@
-name: CI-unixish
-
-on: [push, pull_request]
-
-permissions:
-  contents: read
-
-jobs:
-  build:
-
-    strategy:
-      matrix:
-        os: [ubuntu-22.04, ubuntu-24.04, macos-13, macos-14, macos-15]
-        compiler: [clang++]
-        include:
-          - os: ubuntu-22.04
-            compiler: g++
-          - os: ubuntu-24.04
-            compiler: g++
-      fail-fast: false
-
-    runs-on: ${{ matrix.os }}
-
-    env:
-      CXX: ${{ matrix.compiler }}
-
-    steps:
-    - uses: actions/checkout@v4
-      with:
-        persist-credentials: false
-
-    # the man-db trigger causes package installations to stall for several minutes at times. so just drop the package.
-    # see https://github.com/actions/runner/issues/4030
-    - name: Remove man-db package on ubuntu
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-        sudo apt-get update
-        sudo apt-get remove man-db
-
-    - name: Install missing software on ubuntu
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-          sudo apt-get update
-          sudo apt-get install valgrind
-
-    - name: Install missing software on ubuntu (clang++)
-      if: contains(matrix.os, 'ubuntu') && matrix.compiler == 'clang++'
-      run: |
-        sudo apt-get update
-        sudo apt-get install libc++-dev
-
-      # coreutils contains "nproc"
-    - name: Install missing software on macos
-      if: contains(matrix.os, 'macos')
-      run: |
-        brew install coreutils
-
-    - name: Install missing Python packages
-      run: |
-        python3 -m pip config set global.break-system-packages true
-        python3 -m pip install pytest
-
-    - name: make simplecpp
-      run: make -j$(nproc) CXXOPTS="-Werror"
-
-    - name: make test
-      run: make -j$(nproc) test CXXOPTS="-Werror"
-
-    - name: selfcheck
-      run: |
-        make -j$(nproc) selfcheck
-
-    - name: make testrunner (c++17)
-      run: |
-        make clean
-        make -j$(nproc) testrunner CXXOPTS="-std=c++17"
-
-    - name: make testrunner (c++20)
-      run: |
-        make clean
-        make -j$(nproc) testrunner CXXOPTS="-std=c++20"
-
-    - name: Run CMake
-      run: |
-        cmake -S . -B cmake.output -Werror=dev --warn-uninitialized -DCMAKE_COMPILE_WARNING_AS_ERROR=On
-
-    - name: CMake simplecpp
-      run: |
-        cmake --build cmake.output --target simplecpp -- -j $(nproc)
-
-    - name: CMake testrunner
-      run: |
-        cmake --build cmake.output --target testrunner -- -j $(nproc)
-        ./cmake.output/testrunner
-        # Re-run tests from within the build directory to validate that
-        # SIMPLECPP_TEST_SOURCE_DIR is correctly defined and resolved
-        (cd cmake.output && ./testrunner)
-
-    - name: Run valgrind
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-          make clean
-          make -j$(nproc) CXXOPTS="-O1"
-          valgrind --leak-check=full --num-callers=50 --show-reachable=yes --track-origins=yes --gen-suppressions=all --error-exitcode=42 ./testrunner
-          # TODO: run Python tests with valgrind
-          VALGRIND_TOOL=memcheck ./selfcheck.sh
-
-    - name: Run with libstdc++ debug mode
-      if: matrix.os == 'ubuntu-24.04' && matrix.compiler == 'g++'
-      run: |
-        make clean
-        make -j$(nproc) test selfcheck CXXOPTS="-Werror -g3 -D_GLIBCXX_DEBUG"
-
-    - name: Run with libc++ hardening mode
-      if: matrix.os == 'ubuntu-24.04' && matrix.compiler == 'clang++'
-      run: |
-        make clean
-        make -j$(nproc) test selfcheck CXXOPTS="-Werror -stdlib=libc++ -g3 -D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG" LDOPTS="-lc++"
-
-    - name: Run AddressSanitizer
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-        make clean
-        make -j$(nproc) test selfcheck CXXOPTS="-Werror -O2 -g3 -fsanitize=address" LDOPTS="-fsanitize=address"
-      env:
-        ASAN_OPTIONS: detect_stack_use_after_return=1
-
-    - name: Run UndefinedBehaviorSanitizer
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-        make clean
-        make -j$(nproc) test selfcheck CXXOPTS="-Werror -O2 -g3 -fsanitize=undefined -fno-sanitize=signed-integer-overflow" LDOPTS="-fsanitize=undefined -fno-sanitize=signed-integer-overflow"
-      env:
-        UBSAN_OPTIONS: print_stacktrace=1:halt_on_error=1:report_error_type=1
-
-    # TODO: requires instrumented libc++
-    - name: Run MemorySanitizer
-      if: false && matrix.os == 'ubuntu-24.04' && matrix.compiler == 'clang++'
-      run: |
-        make clean
-        make -j$(nproc) test selfcheck CXXOPTS="-Werror -O2 -g3 -stdlib=libc++ -fsanitize=memory" LDOPTS="-lc++ -fsanitize=memory"
-
-    - name: Run callgrind
-      if: matrix.os == 'ubuntu-24.04'
-      run: |
-        wget https://github.com/danmar/simplecpp/archive/refs/tags/1.5.1.tar.gz
-        tar xvf 1.5.1.tar.gz
-        make clean
-        make -j$(nproc) CXXOPTS="-O2 -g3"
-        VALGRIND_TOOL=callgrind SIMPLECPP_PATH=simplecpp-1.5.1 ./selfcheck.sh >callgrind.log || (cat callgrind.log && false)
-        cat callgrind.log
-        for f in callgrind.out.*;
-        do
-          callgrind_annotate --auto=no $f > $f.annotated.log
-          head -50 $f.annotated.log
-        done
-
-    - uses: actions/upload-artifact@v4
-      if: matrix.os == 'ubuntu-24.04'
-      with:
-        name: Callgrind Output - ${{ matrix.compiler }}
-        path: |
-          ./callgrind.*
diff --git a/.github/workflows/CI-windows.yml b/.github/workflows/CI-windows.yml
deleted file mode 100644
index ccf208fa..00000000
--- a/.github/workflows/CI-windows.yml
+++ /dev/null
@@ -1,66 +0,0 @@
-# Some convenient links:
-# - https://github.com/actions/virtual-environments/blob/master/images/win/Windows2019-Readme.md
-#
-
-name: CI-windows
-
-on: [push,pull_request]
-
-permissions:
-  contents: read
-
-defaults:
-  run:
-    shell: cmd
-    
-jobs:
-
-  build:
-    strategy:
-      matrix:
-        os: [windows-2022, windows-2025, windows-11-arm]
-        config: [Release, Debug]
-      fail-fast: false
-
-    runs-on: ${{ matrix.os }}
-
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          persist-credentials: false
-
-      - name: Setup msbuild.exe
-        uses: microsoft/setup-msbuild@v2
-
-      - name: Set up Python 3.13
-        uses: actions/setup-python@v5
-        with:
-          python-version: '3.13'
-          check-latest: true
-
-      - name: Install missing Python packages
-        run: |
-          python -m pip install pip --upgrade || exit /b !errorlevel!
-          python -m pip install pytest || exit /b !errorlevel!
-
-      - name: Run CMake
-        run: |
-          cmake -G "Visual Studio 17 2022" -A x64 -Werror=dev --warn-uninitialized -DCMAKE_COMPILE_WARNING_AS_ERROR=On . || exit /b !errorlevel!
-
-      - name: Build
-        run: |
-           msbuild -m simplecpp.sln /p:Configuration=${{ matrix.config }} /p:Platform=x64 || exit /b !errorlevel!
-           
-      - name: Test
-        run: |
-          .\${{ matrix.config }}\testrunner.exe || exit /b !errorlevel!
-
-      - name: Selfcheck
-        run: |
-          .\${{ matrix.config }}\simplecpp.exe simplecpp.cpp -e || exit /b !errorlevel!
-
-      - name: integration test
-        run: |
-          set SIMPLECPP_EXE_PATH=.\${{ matrix.config }}\simplecpp.exe
-          python -m pytest integration_test.py -vv || exit /b !errorlevel!
-        
diff --git a/.github/workflows/clang-tidy.yml b/.github/workflows/clang-tidy.yml
deleted file mode 100644
index 4b52d7bc..00000000
--- a/.github/workflows/clang-tidy.yml
+++ /dev/null
@@ -1,51 +0,0 @@
-# Syntax reference https://help.github.com/en/actions/reference/workflow-syntax-for-github-actions
-# Environment reference https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners
-name: clang-tidy
-
-on: [push, pull_request]
-
-permissions:
-  contents: read
-
-jobs:
-  build:
-
-    runs-on: ubuntu-24.04
-
-    steps:
-      - uses: actions/checkout@v4
-        with:
-          persist-credentials: false
-
-      # the man-db trigger causes package installations to stall for several minutes at times. so just drop the package.
-      # see https://github.com/actions/runner/issues/4030
-      - name: Remove man-db package
-        run: |
-          sudo apt-get update
-          sudo apt-get remove man-db
-
-      - name: Install missing software
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y cmake make
-
-      - name: Install clang
-        run: |
-          wget https://apt.llvm.org/llvm.sh
-          chmod +x llvm.sh
-          sudo ./llvm.sh 21
-          sudo apt-get install clang-tidy-21
-
-      - name: Verify clang-tidy configuration
-        run: |
-          clang-tidy-21 --verify-config
-
-      - name: Prepare CMake
-        run: |
-          cmake -S . -B cmake.output -Werror=dev --warn-uninitialized -DCMAKE_COMPILE_WARNING_AS_ERROR=On -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
-        env:
-          CXX: clang-21
-
-      - name: Clang-Tidy
-        run: |
-          run-clang-tidy-21 -q -j $(nproc) -p=cmake.output
diff --git a/.github/workflows/format.yml b/.github/workflows/format.yml
deleted file mode 100644
index 4d5657f8..00000000
--- a/.github/workflows/format.yml
+++ /dev/null
@@ -1,62 +0,0 @@
-# Syntax reference https://help.github.com/en/actions/reference/workflow-syntax-for-github-actions
-# Environment reference https://help.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners
-name: format
-
-on:
-  push:
-    branches:
-      - 'master'
-      - 'releases/**'
-      - '1.*'
-    tags:
-      - '1.*'
-  pull_request:
-
-permissions:
-  contents: read
-
-jobs:
-  format:
-
-    runs-on: ubuntu-22.04
-
-    defaults:
-      run:
-        shell: bash -euo pipefail {0}
-
-    env:
-      UNCRUSTIFY_INSTALL_DIR: ${{ github.workspace }}/runformat-uncrustify
-
-    steps:
-      - uses: actions/checkout@v5
-        with:
-          persist-credentials: false
-
-      - name: Determine uncrustify version
-        id: get-uncrustify-version
-        run: |
-          version="$(./runformat --expected-uncrustify-version)"
-          echo "Expected uncrustify version: $version"
-          echo "version=$version" >> "$GITHUB_OUTPUT"
-
-      - name: Set UNCRUSTIFY_VERSION env variable
-        run: |
-          version=$(./runformat --expected-uncrustify-version)
-          echo "version [$version]"
-          echo "UNCRUSTIFY_VERSION=${version}" >> "$GITHUB_ENV"
-
-      - name: Cache uncrustify
-        uses: actions/cache@v4
-        id: cache-uncrustify
-        with:
-          path: ${{ env.UNCRUSTIFY_INSTALL_DIR }}
-          key: ${{ runner.os }}-uncrustify-${{ steps.get-uncrustify-version.outputs.version }}
-
-      - name: Install uncrustify
-        if: steps.cache-uncrustify.outputs.cache-hit != 'true'
-        run: |
-          ./runformat --install --install-dir "${UNCRUSTIFY_INSTALL_DIR}"
-
-      - name: Uncrustify check
-        run: |
-          ./runformat
diff --git a/CMakeLists.txt b/CMakeLists.txt
index efdc0d96..d91a7c2e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,7 +37,9 @@ if (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
     add_compile_options(-Woverloaded-virtual)       # when a function declaration hides virtual functions from a base class
 
     add_compile_options(-Wsuggest-attribute=noreturn)
-    add_compile_options_safe(-Wuseless-cast)
+    if (NOT MINGW)
+        add_compile_options_safe(-Wuseless-cast)  # triggered by _WIN32 code
+    endif()
 elseif (CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
     add_compile_definitions(_CRT_SECURE_NO_WARNINGS)
     # TODO: bump warning level
@@ -62,6 +64,13 @@ elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     add_compile_options(-Wno-suggest-destructor-override)
     # contradicts -Wcovered-switch-default
     add_compile_options(-Wno-switch-default)
+    if (MINGW)
+        add_compile_options(-Wno-reserved-macro-identifier)
+        add_compile_options(-Wno-unused-macros)
+    endif()
+    # these are experimental warning which might produce false positives
+    add_compile_options_safe(-Wno-thread-safety-negative)
+    add_compile_options_safe(-Wno-thread-safety-beta)
     # TODO: fix these?
     add_compile_options(-Wno-padded)
     add_compile_options(-Wno-sign-conversion)
diff --git a/selfcheck.sh b/selfcheck.sh
index e708023a..b2129cc9 100755
--- a/selfcheck.sh
+++ b/selfcheck.sh
@@ -41,16 +41,20 @@ if [ "$cxx_type" = "Ubuntu" ] || [ "$cxx_type" = "Debian" ]; then
 fi
 
 # TODO: generate defines from compiler
-if [ "$cxx_type" = "g++" ]; then
+if [ "$cxx_type" = "g++" ] || [ "$cxx_type" = "g++.exe" ]; then
   defs=
   defs="$defs -D__GNUC__"
   defs="$defs -D__STDC__"
   defs="$defs -D__x86_64__"
   defs="$defs -D__STDC_HOSTED__"
   defs="$defs -D__CHAR_BIT__=8"
+  if [ "${MSYSTEM}" = "MINGW32" ] || [ "${MSYSTEM}" = "MINGW64" ]; then
+    defs="$defs -D_WIN32"
+  fi
   defs="$defs -D__has_builtin(x)=(1)"
   defs="$defs -D__has_cpp_attribute(x)=(1)"
   defs="$defs -D__has_attribute(x)=(1)"
+  defs="$defs -Ddefined(x)=(0)"
 
   inc=
   while read line
@@ -63,12 +67,19 @@ elif [ "$cxx_type" = "clang" ]; then
   defs="$defs -D__x86_64__"
   defs="$defs -D__STDC_HOSTED__"
   defs="$defs -D__CHAR_BIT__=8"
+  defs="$defs -D__BYTE_ORDER__=1234"
+  defs="$defs -D__SIZEOF_SIZE_T__=8"
+  if [ "${MSYSTEM}" = "MINGW32" ] || [ "${MSYSTEM}" = "MINGW64" ] || [ "${MSYSTEM}" = "CLANG64" ]; then
+    defs="$defs -D_WIN32"
+  fi
   defs="$defs -D__has_builtin(x)=(1)"
   defs="$defs -D__has_cpp_attribute(x)=(1)"
   defs="$defs -D__has_feature(x)=(1)"
-  defs="$defs -D__has_include_next(x)=(0)"
+  defs="$defs -D__has_include_next(x)=(1)"
   defs="$defs -D__has_attribute(x)=(0)"
   defs="$defs -D__building_module(x)=(0)"
+  defs="$defs -D__has_extension(x)=(1)"
+  defs="$defs -Ddefined(x)=(0)"
 
   inc=
   while read line
diff --git a/simplecpp.cpp b/simplecpp.cpp
index d5b51080..bca4b9e0 100644
--- a/simplecpp.cpp
+++ b/simplecpp.cpp
@@ -3122,7 +3122,7 @@ std::pair<simplecpp::FileData *, bool> simplecpp::FileDataCache::get(const std::
 bool simplecpp::FileDataCache::getFileId(const std::string &path, FileID &id)
 {
 #ifdef _WIN32
-    HANDLE hFile = CreateFileA(path.c_str(), 0, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+    HANDLE hFile = CreateFileA(path.c_str(), 0, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
 
     if (hFile == INVALID_HANDLE_VALUE)
         return false;
diff --git a/test.cpp b/test.cpp
index 26e3b95b..dbfede84 100644
--- a/test.cpp
+++ b/test.cpp
@@ -3257,7 +3257,7 @@ static void safe_api()
 }
 
 static void isAbsolutePath() {
-#ifdef _WIN32
+#if defined(_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__)
     ASSERT_EQUALS(true, simplecpp::isAbsolutePath("C:\\foo\\bar"));
     ASSERT_EQUALS(true, simplecpp::isAbsolutePath("C:/foo/bar"));
     ASSERT_EQUALS(true, simplecpp::isAbsolutePath("\\\\foo\\bar"));