diff --git a/.github/workflows/mingw.yml b/.github/workflows/mingw.yml
new file mode 100644
index 00000000..e8cc5b6e
--- /dev/null
+++ b/.github/workflows/mingw.yml
@@ -0,0 +1,73 @@
+name: MSYS2 build
+
+on: push
+
+jobs:
+  mingw:
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        sys:
+          - mingw64
+          - ucrt64
+          - clang64
+#          - clangarm64
+
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+        with:
+          submodules: 'recursive'
+
+      - name: Setup msys2 and mingw-w64
+        uses: msys2/setup-msys2@v2
+        with:
+          msystem: ${{matrix.sys}}
+          update: true
+          pacboy: >-
+            cmake:p
+            ninja:p
+            toolchain:p
+            cppwinrt:p
+            boost:p
+
+      - name: Build debug
+        shell: msys2 {0}
+        run: |
+          cmake -S . -B build-debug \
+            -DCMAKE_BUILD_TYPE=Debug \
+            -DBUILD_TESTING=1 \
+            -DLIBREMIDI_EXAMPLES=1 \
+            -DLIBREMIDI_TESTS=1 \
+            -DLIBREMIDI_CI=1 \
+            -DCMAKE_CTEST_ARGUMENTS="--rerun-failed;--output-on-failure" \
+            -DCMAKE_INSTALL_PREFIX=install
+
+          cmake --build build-debug
+          cmake --build build-debug --target install
+
+      - name: Test debug
+        shell: msys2 {0}
+        run: |
+          cmake --build build-debug --target test
+
+      - name: Build release
+        shell: msys2 {0}
+        run: |
+          cmake -S . -B build-release \
+            -DCMAKE_BUILD_TYPE=Release \
+            -DBUILD_TESTING=1 \
+            -DLIBREMIDI_EXAMPLES=1 \
+            -DLIBREMIDI_TESTS=1 \
+            -DLIBREMIDI_CI=1 \
+            -DCMAKE_CTEST_ARGUMENTS="--rerun-failed;--output-on-failure" \
+            -DCMAKE_INSTALL_PREFIX=install
+
+          cmake --build build-release
+          cmake --build build-release --target install
+
+      - name: Test release
+        shell: msys2 {0}
+        run: |
+          cmake --build build-release --target test
+
diff --git a/cmake/libremidi.deps.cmake b/cmake/libremidi.deps.cmake
index fe488e79..13c878ca 100644
--- a/cmake/libremidi.deps.cmake
+++ b/cmake/libremidi.deps.cmake
@@ -44,11 +44,11 @@ if(LIBREMIDI_NEEDS_READERWRITERQUEUE AND NOT TARGET readerwriterqueue)
 
   if(NOT readerwriterqueue_FOUND)
     FetchContent_Declare(
-        readerwriterqueue
+        rwq
         GIT_REPOSITORY https://github.com/cameron314/readerwriterqueue
         GIT_TAG        master
     )
 
-    FetchContent_MakeAvailable(readerwriterqueue)
+    FetchContent_MakeAvailable(rwq)
   endif()
 endif()
diff --git a/cmake/libremidi.tests.cmake b/cmake/libremidi.tests.cmake
index 511b1ffb..505381fb 100644
--- a/cmake/libremidi.tests.cmake
+++ b/cmake/libremidi.tests.cmake
@@ -1,7 +1,12 @@
+if(CMAKE_VERSION VERSION_GREATER 3.25)
+    set(CMAKE_FETCHCONTENT_SYSTEM_KEYWORD "SYSTEM")
+endif()
+
 FetchContent_Declare(
     Catch2
     GIT_REPOSITORY https://github.com/catchorg/Catch2.git
     GIT_TAG        v3.4.0
+    ${CMAKE_FETCHCONTENT_SYSTEM_KEYWORD}
 )
 
 FetchContent_MakeAvailable(Catch2)
diff --git a/include/libremidi/backends/winmidi/observer.hpp b/include/libremidi/backends/winmidi/observer.hpp
index 304179e2..3380de44 100644
--- a/include/libremidi/backends/winmidi/observer.hpp
+++ b/include/libremidi/backends/winmidi/observer.hpp
@@ -167,7 +167,7 @@ class observer_impl final
   }
 
   void on_device_updated(
-      const MidiEndpointDeviceWatcher& e,
+      const MidiEndpointDeviceWatcher&,
       const MidiEndpointDeviceInformationUpdatedEventArgs& result)
   {
     // OPTIMIZEME
diff --git a/include/libremidi/backends/winuwp/midi_in.hpp b/include/libremidi/backends/winuwp/midi_in.hpp
index 0ccfbc50..2cd6eeda 100644
--- a/include/libremidi/backends/winuwp/midi_in.hpp
+++ b/include/libremidi/backends/winuwp/midi_in.hpp
@@ -47,7 +47,8 @@ class midi_in_winuwp final
     midi_start_timestamp = std::chrono::steady_clock::now();
 
     port_.MessageReceived(
-        [=](const winrt::Windows::Devices::Midi::IMidiInPort& inputPort,
+        [this](
+            const winrt::Windows::Devices::Midi::IMidiInPort&,
             const winrt::Windows::Devices::Midi::MidiMessageReceivedEventArgs& args) {
       this->process_message(args.Message());
     });
diff --git a/include/libremidi/backends/winuwp/observer.hpp b/include/libremidi/backends/winuwp/observer.hpp
index 7b5d2430..83e7a97f 100644
--- a/include/libremidi/backends/winuwp/observer.hpp
+++ b/include/libremidi/backends/winuwp/observer.hpp
@@ -1,5 +1,6 @@
 #pragma once
 #include <libremidi/backends/winuwp/config.hpp>
+#include <libremidi/backends/winuwp/helpers.hpp>
 #include <libremidi/detail/observer.hpp>
 
 namespace libremidi
@@ -33,11 +34,11 @@ class observer_winuwp_internal
       cbs.emplace_back(tk, f);
       return tk;
     }
+
     void remove(int tk)
     {
       auto it = std::remove_if(
           cbs.begin(), cbs.end(), [tk](const callback& c) { return c.token == tk; });
-      auto r = std::distance(it, cbs.end());
       cbs.erase(it, cbs.end());
     }
   };
@@ -122,7 +123,7 @@ class observer_winuwp_internal
     deviceWatcher_.Added(evTokenOnDeviceAdded_);
   }
 
-  void on_device_added(DeviceWatcher sender, DeviceInformation deviceInfo)
+  void on_device_added(const DeviceWatcher&, const DeviceInformation& deviceInfo)
   {
     port_info p;
     {
@@ -133,7 +134,7 @@ class observer_winuwp_internal
     portAddedEvent_(p);
   }
 
-  void on_device_removed(DeviceWatcher sender, DeviceInformationUpdate deviceUpdate)
+  void on_device_removed(const DeviceWatcher&, const DeviceInformationUpdate& deviceUpdate)
   {
     const auto id = deviceUpdate.Id();
     auto pred = [&id](const port_info& portInfo) { return portInfo.id == id; };
@@ -152,9 +153,9 @@ class observer_winuwp_internal
       portRemovedEvent_(*p);
   }
 
-  void on_device_updated(DeviceWatcher sender, DeviceInformationUpdate deviceUpdate) { }
+  void on_device_updated(const DeviceWatcher&, const DeviceInformationUpdate&) { }
 
-  void on_device_enumeration_completed(DeviceWatcher sender, IInspectable const&) { }
+  void on_device_enumeration_completed(const DeviceWatcher&, const IInspectable&) { }
 
 private:
   std::vector<port_info> portList_;