diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 8bfbe0e8a..256394af7 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -111,7 +111,7 @@ jobs:
       shell: cmd
       run: |
         call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat"
-        rake -E "STDOUT.sync=true" -m -j4 test
+        rake -E "STDOUT.sync=true" test
       env:
         MRUBY_TARGET: appveyor
         # TODO(take-cheeze): Re-enable /O2