diff --git a/.github/workflows/windows-msys2.yml b/.github/workflows/windows-msys2.yml
index 4186964d..34021ceb 100644
--- a/.github/workflows/windows-msys2.yml
+++ b/.github/workflows/windows-msys2.yml
@@ -66,6 +66,7 @@ jobs:
             --disable-intersense
             --prefix=/ssr-files
             CPPFLAGS="-I/ucrt64/include -I`pwd`/../websocketpp -D_WEBSOCKETPP_CPP11_THREAD_"
+            CFLAGS=-mwin32
             LDFLAGS=-L/ucrt64/lib
             LIBS="-lws2_32 -lwsock32 -lglu32 -lopengl32"
           )