diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 52f65fa6..d98a1662 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -33,7 +33,16 @@ jobs:
       - uses: actions/checkout@v2
       - uses: ilammy/msvc-dev-cmd@v1
 
-      - name: Setup
+      - name: install-rtools
+        run: |
+          choco install rtools --no-progress
+          echo "c:\rtools40\ucrt64\bin;" >> $env:GITHUB_PATH
+      - name: show-gfortran
+        run: |
+          gcc --version
+          gfortran --version      - name: Setup
+
+      - name: Set env variables
         run: |
           BITS=${{ matrix.BUILD_BITS }}
           echo "BUILD_BITS=$BITS" >> $GITHUB_ENV;
@@ -45,23 +54,6 @@ jobs:
           echo "START_DIR=$PWD" >> $GITHUB_ENV;
           choco install -y zip
 
-      - run: |
-          choco install -y mingw --forcex86 --force --version=8.1.0
-          choco install -y make
-        name: Install 32-bit mingw
-        shell: powershell
-        if: ${{ matrix.BUILD_BITS == '32' }}
-
-      - run: |
-          # see https://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg586184.html
-          if [ "${{ matrix.BUILD_BITS }}" == "64" ]; then
-            include=/c/ProgramData/Chocolatey/lib/mingw/tools/install/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/avx512fintrin.h
-          else
-            include=/c/ProgramData/Chocolatey/lib/mingw/tools/install/mingw32/lib/gcc/i686-w64-mingw32/8.1.0/include/avx512fintrin.h
-          fi
-          sed -i -e"s/_mm512_abs_pd (__m512 __A)/_mm512_abs_pd (__m512d __A)/" $include
-        name: Fix gcc bug
-
       - name: Build
         run: |
           BITS=${{ matrix.BUILD_BITS }}
diff --git a/tools/build_openblas.ps1 b/tools/build_openblas.ps1
new file mode 100755
index 00000000..aba10dbf
--- /dev/null
+++ b/tools/build_openblas.ps1
@@ -0,0 +1,48 @@
+# Build script for OpenBLAS on Windows
+# Expects environment variables:
+# $OPENBLAS_ROOT="c:\opt\openblas"
+# $INTERFACE64
+# $BITS
+$SUFFIX = "_m64"
+# Expects "gcc" to be on the path
+$march="x86-64"
+# https://csharp.wekeepcoding.com/article/10463345/invalid+register+for+.seh_savexmm+in+Cygwin
+$extra="-fno-asynchronous-unwind-tables"
+$long_double="mlong-double-64"
+$plat_tag="win_amd64"
+$cflags="-O2 -march=$march -mtune=generic $extra $long_double"
+$fflags="$extra $cflags -frecursive -ffpe-summary=invalid,zero $long_double"
+
+# Set suffixed-ILP64 flags
+if [ "$INTERFACE64" == "1" ]; then
+    interface64_flags="INTERFACE64=1 SYMBOLSUFFIX=64_"
+    SYMBOLSUFFIX=64_
+    # We override FCOMMON_OPT, so we need to set default integer manually
+    fflags="$fflags -fdefault-integer-8"
+} else {
+    $interface64_flags = ""
+    $SYMBOL_SUFFIX = ""
+}
+
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90329
+$fflags="$fflags -fno-optimize-sibling-calls"
+
+# Build OpenBLAS
+make BINARY=$BUILD_BITS DYNAMIC_ARCH=1 USE_THREAD=1 USE_OPENMP=0 `
+     NUM_THREADS=24 NO_WARMUP=1 NO_AFFINITY=1 CONSISTENT_FPCSR=1 `
+     BUILD_LAPACK_DEPRECATED=1 TARGET=PRESCOTT BUFFERSIZE=20 `
+     COMMON_OPT="$cflags" `
+     FCOMMON_OPT="$fflags" `
+     LDFLAGS="-lucrt -static" `
+     MAX_STACK_ALLOC=2048 `
+     $interface64_flags
+$out_root="$OPENBLAS_ROOT\if_$IF_BITS$SUFFIX\$BUILD_BITS"
+make PREFIX=$out_root $interface64_flags install
+# Powershell specific?  Paths in pkg-config file lack separators.
+# Patch
+$pkg_cfg_pc = "$out_root\lib\pkgconfig\openblas.pc"
+$unix_out_root = $out_root -replace '\\','/'
+(Get-Content -path $pkg_cfg_pc -Raw)  `
+    -replace "(?m)^libdir=.*$", "libdir=$unix_out_root/lib"  `
+    -replace "(?m)^includedir=.*$", "includedir=$unix_out_root/include"  `
+| Set-Content -Path "${pkg_cfg_pc}"