diff --git a/test/test_mpi_communication.py b/test/test_mpi_communication.py
index 091111ed37c6cf72f12e43f03accaf326b69548f..886099645754f2907afcbb128c36777b98248df5 100644
--- a/test/test_mpi_communication.py
+++ b/test/test_mpi_communication.py
@@ -257,13 +257,11 @@ def test_mpi(num_ranks):
 
     from subprocess import check_call
     import sys
-    newenv = os.environ.copy()
-    newenv["RUN_WITHIN_MPI"] = "1"
-    newenv["TEST_MPI_COMMUNICATION"] = "1"
     check_call([
-        "mpiexec", "-np", str(num_ranks), "-x", "RUN_WITHIN_MPI",
-        sys.executable, __file__],
-        env=newenv)
+        "mpiexec", "-np", str(num_ranks),
+        "-x", "RUN_WITHIN_MPI=1",
+        "-x", "TEST_MPI_COMMUNICATION=1",
+        sys.executable, __file__])
 
 
 @pytest.mark.mpi
@@ -274,13 +272,11 @@ def test_simple_mpi(num_ranks):
 
     from subprocess import check_call
     import sys
-    newenv = os.environ.copy()
-    newenv["RUN_WITHIN_MPI"] = "1"
-    newenv["TEST_SIMPLE_MPI_COMMUNICATION"] = "1"
     check_call([
-        "mpiexec", "-np", str(num_ranks), "-x", "RUN_WITHIN_MPI",
-        sys.executable, __file__],
-        env=newenv)
+        "mpiexec", "-np", str(num_ranks),
+        "-x", "RUN_WITHIN_MPI=1",
+        "-x", "TEST_SIMPLE_MPI_COMMUNICATION=1",
+        sys.executable, __file__])
 
 # }}}