diff --git a/.github/workflows/test_pr_and_main.yml b/.github/workflows/test_pr_and_main.yml
index 702edd280..dcef8da32 100644
--- a/.github/workflows/test_pr_and_main.yml
+++ b/.github/workflows/test_pr_and_main.yml
@@ -26,7 +26,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: chartboost/ruff-action@v1
+      # Pin the ruff version: an unpinned linter means an upstream release
+      # can turn every PR red overnight (ruff 0.16.0 did exactly that by
+      # expanding the default rule set).  Bump deliberately.
+      - uses: astral-sh/ruff-action@v3
+        with:
+          version: "0.15.21"
 
   nompi4py:
     name: no mpi4py