diff --git a/tests/checksum/backend/openpmd_backend.py b/tests/checksum/backend/openpmd_backend.py
index b6fb600f15..363f322192 100644
--- a/tests/checksum/backend/openpmd_backend.py
+++ b/tests/checksum/backend/openpmd_backend.py
@@ -17,7 +17,7 @@ def __init__(self, filename):
         ''' Constructor: store the dataset object
         '''
 
-        self.dataset = OpenPMDTimeSeries(filename)
+        self.dataset = OpenPMDTimeSeries(filename, backend='h5py')
 
     def fields_list(self):
         ''' Return the list of fields defined on the grid