diff --git a/test/test_partition.py b/test/test_partition.py
index 78258f4f1a0becdba402e32f68b05f0d5fa52ac0..8dd2399773d471d7b7c578601df49c148ff495fe 100644
--- a/test/test_partition.py
+++ b/test/test_partition.py
@@ -531,13 +531,12 @@ def test_mpi_communication(num_partitions, order):
     num_ranks = num_partitions
     from subprocess import check_call
     import sys
-    newenv = os.environ.copy()
-    newenv["RUN_WITHIN_MPI"] = "1"
-    newenv["order"] = str(order)
     check_call([
-        "mpiexec", "-np", str(num_ranks), "-x", "RUN_WITHIN_MPI",
+        "mpiexec", "-np", str(num_ranks),
+        "-x", "RUN_WITHIN_MPI=1",
+        "-x", "order=%d" % order,
         sys.executable, __file__],
-        env=newenv)
+        )
 
 # }}}