diff --git a/bitshuffle/tests/test_h5filter.py b/bitshuffle/tests/test_h5filter.py
index 6739b998..c7361f06 100644
--- a/bitshuffle/tests/test_h5filter.py
+++ b/bitshuffle/tests/test_h5filter.py
@@ -23,7 +23,7 @@ def test_filter(self):
         dtype = np.int64
         data = np.arange(shape[0])
         fname = "tmp_test_filters.h5"
-        f = h5py.File(fname)
+        f = h5py.File(fname, "w")
         h5.create_dataset(f, b"range", shape, dtype, chunks,
                 filter_pipeline=(32008, 32000),
                 filter_flags=(h5z.FLAG_MANDATORY, h5z.FLAG_MANDATORY),
@@ -43,7 +43,7 @@ def test_with_block_size(self):
         dtype = np.int64
         data = np.arange(shape[0])
         fname = "tmp_test_filters.h5"
-        f = h5py.File(fname)
+        f = h5py.File(fname, "w")
         h5.create_dataset(f, b"range", shape, dtype, chunks,
                 filter_pipeline=(32008, 32000),
                 filter_flags=(h5z.FLAG_MANDATORY, h5z.FLAG_MANDATORY),
@@ -65,7 +65,7 @@ def test_with_compression(self):
         dtype = np.int64
         data = np.arange(shape[0])
         fname = "tmp_test_filters.h5"
-        f = h5py.File(fname)
+        f = h5py.File(fname, "w")
         h5.create_dataset(f, b"range", shape, dtype, chunks,
                 filter_pipeline=(32008,),
                 filter_flags=(h5z.FLAG_MANDATORY,),
diff --git a/bitshuffle/tests/test_h5plugin.py b/bitshuffle/tests/test_h5plugin.py
index 7cc195ee..be0d09bc 100644
--- a/bitshuffle/tests/test_h5plugin.py
+++ b/bitshuffle/tests/test_h5plugin.py
@@ -34,8 +34,7 @@ def test_plugins(self):
         dtype = np.int64
         data = np.arange(shape[0])
         fname = "tmp_test_filters.h5"
-        f = h5py.File(fname)
-        f = h5py.File(fname)
+        f = h5py.File(fname, "w")
         dset = f.create_dataset("range",
                 shape=shape,
                 dtype=dtype,