diff --git a/tests/testing_harness.py b/tests/testing_harness.py
index 6d35ef9786..ced1a653f7 100644
--- a/tests/testing_harness.py
+++ b/tests/testing_harness.py
@@ -66,7 +66,7 @@ class TestHarness(object):
 
     def _run_openmc(self):
         if self._opts.mpi_exec:
-            mpi_procs = int(self._opts.mpi_np)
+            mpi_procs = self._opts.mpi_np
         else:
             mpi_procs = 1