diff --git a/tests/cunit/CMakeLists.txt b/tests/cunit/CMakeLists.txt
index 9fabd8fa0a8..599754a708c 100644
--- a/tests/cunit/CMakeLists.txt
+++ b/tests/cunit/CMakeLists.txt
@@ -165,6 +165,7 @@ set (AT_LEAST_TWO_TASKS 3)
 set (AT_LEAST_THREE_TASKS 4)
 set (AT_LEAST_FOUR_TASKS 5)
 set (AT_LEAST_EIGHT_TASKS 9)
+set (EXACTLY_FOUR_TASKS 4)
 
 if (PIO_USE_MPISERIAL)
   add_test(NAME test_pioc
@@ -322,7 +323,7 @@ else ()
     TIMEOUT ${DEFAULT_TEST_TIMEOUT})
   add_mpi_test(test_simple
     EXECUTABLE ${CMAKE_CURRENT_BINARY_DIR}/test_simple
-    NUMPROCS ${AT_LEAST_FOUR_TASKS}
+    NUMPROCS ${EXACTLY_FOUR_TASKS}
     TIMEOUT ${DEFAULT_TEST_TIMEOUT})
 endif ()
 MESSAGE("CMAKE_EXE_LINKER_FLAGS ${CMAKE_EXE_LINKER_FLAGS}")