diff --git a/cmake/Tests.cmake b/cmake/Tests.cmake
index b085c2ba7..56d150417 100644
--- a/cmake/Tests.cmake
+++ b/cmake/Tests.cmake
@@ -8,7 +8,8 @@ if(NOT CTEST_PARALLEL_LEVEL)
   if(NOT CTEST_PARALLEL_LEVEL)
     include(ProcessorCount)
     ProcessorCount(CORES)
-    set(CTEST_PARALLEL_LEVEL ${CORES})
+    math(EXPR halfcores "${CORES} / 2")
+    set(CTEST_PARALLEL_LEVEL ${halfcores})
   endif()
 endif()