diff --git a/tests/sample-data/cams-egg4-monthly.grib b/tests/sample-data/cams-egg4-monthly.grib
new file mode 100644
index 00000000..5af77c33
Binary files /dev/null and b/tests/sample-data/cams-egg4-monthly.grib differ
diff --git a/tests/sample-data/era5-levels-members.nc b/tests/sample-data/era5-levels-members.nc
index 9e52bd77..866410d3 100644
Binary files a/tests/sample-data/era5-levels-members.nc and b/tests/sample-data/era5-levels-members.nc differ
diff --git a/tests/test_50_sample_data.py b/tests/test_50_sample_data.py
index 49765d28..9ea09a58 100644
--- a/tests/test_50_sample_data.py
+++ b/tests/test_50_sample_data.py
@@ -120,3 +120,12 @@ def test_dataset_missing_field_values() -> None:
     t2 = res.variables["t2m"]
     assert np.isclose(np.nanmean(t2[0, :, :]), 268.375)
     assert np.isclose(np.nanmean(t2[1, :, :]), 270.716)
+
+
+def test_valid_month_time_dim() -> None:
+    
+    test_file = os.path.join(SAMPLE_DATA_FOLDER, "cams-egg4-monthly.grib")
+    ds = xr.open_dataset(test_file, time_dims=["valid_month"])
+
+    assert "valid_month" in ds.dims
+