diff --git a/test/test_meshmode.py b/test/test_meshmode.py
index be66f28dab3ea82666e74c7475c4d675cb5c939f..6b6c7b2e1067931b55963672a327f9fa798a9324 100644
--- a/test/test_meshmode.py
+++ b/test/test_meshmode.py
@@ -57,8 +57,7 @@ def test_mpi_communication(num_partitions):
     import os
     newenv = os.environ.copy()
     newenv["PYTOOLS_RUN_WITHIN_MPI"] = "1"
-    check_call(["mpirun", "-np", str(num_ranks),
-                sys.executable, "test/testmpi.py", str(num_partitions)],
+    check_call(["mpirun", "-np", str(num_ranks), sys.executable, "testmpi.py"],
                env=newenv)
 
 
diff --git a/test/testmpi.py b/test/testmpi.py
index 7f84e5015a61743afbd9e63b08a03d314dc5a7b2..511b1fe98030ee226bce74ce19274d546b704be0 100644
--- a/test/testmpi.py
+++ b/test/testmpi.py
@@ -2,11 +2,12 @@ from __future__ import division, absolute_import, print_function
 import numpy as np
 
 
-def mpi_comm(num_parts):
+def mpi_comm():
 
     from mpi4py import MPI
     comm = MPI.COMM_WORLD
     rank = comm.Get_rank()
+    num_parts = comm.Get_size() - 1
 
     # This rank only partitions a mesh and sends them to their respective ranks.
     if rank == 0:
@@ -125,9 +126,4 @@ def mpi_comm(num_parts):
 
 
 if __name__ == "__main__":
-    import sys
-
-    assert len(sys.argv) == 2, 'Invalid number of arguments'
-
-    num_parts = int(sys.argv[1])
-    mpi_comm(num_parts)
+    mpi_comm()