diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 61df8d8..05dc34d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -101,9 +101,13 @@ jobs:
           version: 1.0
 
       - name: Measure performance (Callgrind instructions)
+        # Timeout 600 (was 300): edit_distance/test_case_5 (~45B Ir)
+        # sits on the 300s wall-clock knife-edge under callgrind with
+        # --jobs 2, and shard rotation after #2 tipped it to
+        # usually-timeout. 2x headroom; genuine hangs still fail.
         run: |
           python3 tools/measure.py --resources tests/resources \
-            --repeat 1 --jobs 2 --timeout 300 \
+            --repeat 1 --jobs 2 --timeout 600 \
             --shard ${{ matrix.shard }}/4 \
             --output perf-results.json --bmf-output bencher-bmf.json \
             --summary-file "$GITHUB_STEP_SUMMARY"