diff --git a/.github/workflows/pr_tests.yml b/.github/workflows/pr_tests.yml
index 040d49a87..24b86a30e 100644
--- a/.github/workflows/pr_tests.yml
+++ b/.github/workflows/pr_tests.yml
@@ -44,7 +44,7 @@ jobs:
         run: |
           BINDINGS_HASH=$(git rev-parse HEAD:vendor/logos-delivery-python-bindings)
           DELIVERY_HASH=$(git -C vendor/logos-delivery-python-bindings rev-parse HEAD:vendor/logos-delivery)
-          echo "key=liblogosdelivery-${{ runner.os }}-nim2.2.4-v2-${BINDINGS_HASH}-${DELIVERY_HASH}" >> "$GITHUB_OUTPUT"
+          echo "key=liblogosdelivery-${{ runner.os }}-nim2.2.4-v3-${BINDINGS_HASH}-${DELIVERY_HASH}" >> "$GITHUB_OUTPUT"
 
       - name: Cache liblogosdelivery.so
         id: cache-lib
@@ -106,7 +106,16 @@ jobs:
           # `nimble setup --localdeps` (build-deps prerequisite); a bare
           # `nimble install -y` here is redundant and pulls Nim from the lock,
           # which is what triggered the checksum mismatch.
-          make liblogosdelivery
+          #
+          # -d:disableMarchNative: without it config.nims compiles with
+          # -march=native, and the cached .so then crashes with SIGILL
+          # ("Illegal instruction") when a later job lands on a runner with
+          # an older CPU generation. -d:marchOptimized keeps a portable
+          # x86-64-v2 baseline, which all GitHub-hosted runners support.
+          # Passed via the environment (not a make argument) so the
+          # Makefile's own NIM_PARAMS appends (-d:release, git_version)
+          # still apply.
+          NIM_PARAMS="-d:disableMarchNative -d:marchOptimized" make liblogosdelivery
 
           SO_PATH="$(find . -type f -name 'liblogosdelivery.so' | head -n 1)"