diff --git a/hysop/operator/hdf_io.py b/hysop/operator/hdf_io.py
index cbf67a18e2de4be7b198388f2a0d214e081e666e..cadbcb95938c2ef3fb2012d6f7f5671916b7dfef 100755
--- a/hysop/operator/hdf_io.py
+++ b/hysop/operator/hdf_io.py
@@ -375,10 +375,10 @@ class HDF_Writer(HDF_IO):
         msg = 'count < 0, simu must be initialized.'
         assert i >= 0, msg
         if (self.topology.cart_size == 1) or self.use_parallel_hdf5:
-            return self.io_params.filename + "_{0:05d}".format(i) + '.h5'
+            return self.io_params.filename + "_{0:06d}".format(i) + '.h5'
         else:
             assert self.use_local_hdf5
-            return self.io_params.filename + "_{0:05d}".format(i) + "_rk{rk:03d}.h5"
+            return self.io_params.filename + "_{0:06d}".format(i) + "_rk{rk:04d}.h5"
 
 
     @op_apply