diff --git a/ann_benchmarks/datasets.py b/ann_benchmarks/datasets.py
index ad80eca..33da4a5 100644
--- a/ann_benchmarks/datasets.py
+++ b/ann_benchmarks/datasets.py
@@ -35,7 +35,7 @@ def get_dataset(which):
             print("Creating dataset locally")
             DATASETS[which](hdf5_fn)
 
-    hdf5_f = h5sparse.File(hdf5_fn)
+    hdf5_f = h5sparse.File(hdf5_fn, 'r')
     return hdf5_f