diff --git a/cmake/setup_ult_global_flags.cmake b/cmake/setup_ult_global_flags.cmake
index 17a68cdd6f..ae9055cdb4 100644
--- a/cmake/setup_ult_global_flags.cmake
+++ b/cmake/setup_ult_global_flags.cmake
@@ -14,8 +14,8 @@ if(MSVC)
 else()
   string(TOUPPER ${CMAKE_BUILD_TYPE} CMAKE_BUILD_TYPE_upper)
 
-  string(REGEX REPLACE "-O[1-3]" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
-  string(REGEX REPLACE "-O[1-3]" "" CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE_upper} ${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE_upper}})
+  string(REGEX REPLACE "-O[1-3]" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+  string(REGEX REPLACE "-O[1-3]" "" CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE_upper} "${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE_upper}}")
   #disable fortify source as this requires optimization to be on
   string(REPLACE "-Wp,-D_FORTIFY_SOURCE=2" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
   string(REPLACE "-D_FORTIFY_SOURCE=2" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})