diff --git a/cmake/unit_test.cmake b/cmake/unit_test.cmake
index 2636d4e993e..2d652c90466 100644
--- a/cmake/unit_test.cmake
+++ b/cmake/unit_test.cmake
@@ -1,3 +1,13 @@
+if(EXISTS ${MPIEXEC})
+  # OpenMPI 3.0 and higher checks the number of processes against the number of CPUs
+  execute_process(COMMAND ${MPIEXEC} --version RESULT_VARIABLE mpi_version_result OUTPUT_VARIABLE mpi_version_output ERROR_VARIABLE mpi_version_output)
+  if (mpi_version_result EQUAL 0 AND mpi_version_output MATCHES "\\(Open(RTE| MPI)\\) ([3-9]\\.|1[0-9])")
+    set(MPIEXEC_OVERSUBSCRIBE "-oversubscribe")
+  else()
+    set(MPIEXEC_OVERSUBSCRIBE "")
+  endif()
+endif()
+
 # unit_test function
 function(UNIT_TEST)
   cmake_parse_arguments(TEST "" "NAME;NUM_PROC" "SRC;DEPENDS" ${ARGN})
@@ -31,13 +41,6 @@ function(UNIT_TEST)
       endif()
     endif()
 
-    # OpenMPI 3.0 and higher checks the number of processes against the number of CPUs
-    execute_process(COMMAND ${MPIEXEC} --version RESULT_VARIABLE mpi_version_result OUTPUT_VARIABLE mpi_version_output ERROR_VARIABLE mpi_version_output)
-    if (mpi_version_result EQUAL 0 AND mpi_version_output MATCHES "\\(Open(RTE| MPI)\\) ([3-9]\\.|1[0-9])")
-      set(MPIEXEC_OVERSUBSCRIBE "-oversubscribe")
-    else()
-      set(MPIEXEC_OVERSUBSCRIBE "")
-    endif()
     add_test(${TEST_NAME} ${MPIEXEC} ${MPIEXEC_OVERSUBSCRIBE} ${MPIEXEC_NUMPROC_FLAG} ${TEST_NUM_PROC} ${MPIEXEC_PREFLAGS} ${CMAKE_CURRENT_BINARY_DIR}/${TEST_NAME} ${MPIEXEC_POSTFLAGS})
   else( )
     add_test(${TEST_NAME} ${TEST_NAME})