diff --git a/CMakeLists.txt b/CMakeLists.txt
index 07c31d497..de1c23e91 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -109,6 +109,8 @@ find_package(StandardMathLibrary)
 
 set(EIGEN_TEST_CUSTOM_LINKER_FLAGS  "" CACHE STRING "Additional linker flags when linking unit tests.")
 set(EIGEN_TEST_CUSTOM_CXX_FLAGS     "" CACHE STRING "Additional compiler flags when compiling unit tests.")
+# convert space separated argument into CMake lists for downstream consumption
+separate_arguments(EIGEN_TEST_CUSTOM_CXX_FLAGS NATIVE_COMMAND ${EIGEN_TEST_CUSTOM_CXX_FLAGS})
 
 set(EIGEN_STANDARD_LIBRARIES_TO_LINK_TO "")
 
diff --git a/cmake/EigenTesting.cmake b/cmake/EigenTesting.cmake
index c8bc915a6..35819411d 100644
--- a/cmake/EigenTesting.cmake
+++ b/cmake/EigenTesting.cmake
@@ -79,7 +79,7 @@ macro(ei_add_test_internal testname testname_with_suffix)
   endif()
 
   if(EIGEN_TEST_CUSTOM_CXX_FLAGS)
-    target_compile_options(${targetname} PRIVATE "${EIGEN_TEST_CUSTOM_CXX_FLAGS}")
+    target_compile_options(${targetname} PRIVATE ${EIGEN_TEST_CUSTOM_CXX_FLAGS})
   endif()
 
   if(EIGEN_STANDARD_LIBRARIES_TO_LINK_TO)