diff --git a/hysop/operator/tests/test_directional_advection.py b/hysop/operator/tests/test_directional_advection.py
index 13184b08800c0b90a5fb64996b1486b30bfc3653..9463d3745899f5668bdcf916e8a5a3e58d0d7449 100644
--- a/hysop/operator/tests/test_directional_advection.py
+++ b/hysop/operator/tests/test_directional_advection.py
@@ -217,11 +217,14 @@ class TestDirectionalAdvectionOperator(object):
                                 if npw.any(d > 1e-1):
                                     print 'FATAL ERROR: Could not match analytic advection.'
                                     print 'DSOUT'
-                                    print dsout.sdata[dsout.compute_slices]
+                                    for output in dsout:
+                                        print output.sdata[output.compute_slices]
                                     print 'DSREF'
-                                    print dsref.sdata[dsref.compute_slices]
+                                    for ref in dsref:
+                                        print ref.sdata[ref.compute_slices]
                                     print 'DSREF - DSOUT'
-                                    print (dsout.sdata[dsout.compute_slices].get() - dsref.sdata[dsref.compute_slices].get())
+                                    for (output, ref) in zip(dsout, dsref):
+                                        print (output.sdata[output.compute_slices].get() - ref.sdata[ref.compute_slices].get())
                                     msg='Test failed with V={}, k={}, dxk={}, inter-field L2 distances are {}.' 
                                     msg=msg.format(Vi, k, to_tuple(dxk, cast=float), to_tuple(d, cast=float))
                                     raise RuntimeError(msg)