diff --git a/.codecov.yml b/.codecov.yml
index b427851db..430a6e498 100644
--- a/.codecov.yml
+++ b/.codecov.yml
@@ -3,6 +3,7 @@ coverage:
     project:
       default:
         target: auto
+        threshold: 10%
     patch:
       default:
         target: 80%
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index f5c4f0248..0f2b54431 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -21,10 +21,10 @@ jobs:
           python-version: "3.12"
 
       - name: Run unit tests with coverage
-        run: poetry run pytest -v tests --ignore tests/integration --cov malariagen_data/anoph --cov-report=xml
+        run: poetry run pytest -v tests --ignore tests/integration --cov malariagen_data --cov-report=xml
 
       - name: Upload coverage report
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           files: ./coverage.xml
           verbose: true
diff --git a/tests/anoph/test_snp_data.py b/tests/anoph/test_snp_data.py
index bcaf58aa8..d981463e4 100644
--- a/tests/anoph/test_snp_data.py
+++ b/tests/anoph/test_snp_data.py
@@ -337,7 +337,7 @@ def test_snp_sites_with_virtual_contigs(ag3_sim_api, chrom):
     check_snp_sites(api, region=region)
 
     # Extra checks.
-    region_size = stop - start
+    region_size = stop - start + 1
     pos = api.snp_sites(region=region, field="POS").compute()
     assert pos.shape[0] <= region_size
     assert np.all(pos >= start)
@@ -1157,7 +1157,8 @@ def check_snp_allele_counts(
     assert ac.shape == (pos.shape[0], 4)
     assert np.all(ac >= 0)
     an = ac.sum(axis=1)
-    assert an.max() <= 2 * n_samples
+    if an.size > 0:
+        assert an.max() <= 2 * n_samples
 
     # Run again to ensure loading from results cache produces the same result.
     ac2 = api.snp_allele_counts(