diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index e2d19603088..bee25d38fec 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -180,7 +180,7 @@ jobs:
       - name: Run tests
         run: |
           python3 ./mach test-wpt \
-            --release --processes $(nproc) --timeout-multiplier 8 \
+            --release --processes $(sysctl -n hw.logicalcpu) --timeout-multiplier 8 \
             --total-chunks ${{ env.max_chunk_id }} --this-chunk ${{ matrix.chunk_id }} \
             --log-raw test-wpt.${{ matrix.chunk_id }}.log \
             --log-servojson wpt-jsonsummary.${{ matrix.chunk_id }}.log \