diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9d0ba64d..431b416a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,7 +34,10 @@ jobs:
 
   test:
     name: Test
-    runs-on: ubuntu-latest
+    # Pinned off ubuntu-latest: its image moved to kernel 6.17, on which
+    # `bun test` SIGILLs (Bun 1.3.5) / mis-resolves ESM (1.3.14). The 24.04
+    # image runs the pinned toolchain cleanly. See #200.
+    runs-on: ubuntu-24.04
     timeout-minutes: 20
     steps:
       - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0