diff --git a/utils.cmake b/utils.cmake
index 22735c7..43222be 100644
--- a/utils.cmake
+++ b/utils.cmake
@@ -119,6 +119,14 @@ function(setup_project)
             set(CMAKE_C_STANDARD_REQUIRED ON PARENT_SCOPE)
             set(CMAKE_C_EXTENSIONS OFF PARENT_SCOPE)
             set(CMAKE_C_VISIBILITY_PRESET "hidden" PARENT_SCOPE)
+            if(NOT DEFINED CMAKE_C_FLAGS)
+                message(WARNING "CMAKE_C_FLAGS is not defined.")
+                set(CMAKE_C_FLAGS)
+            endif()
+            if(NOT DEFINED CMAKE_C_FLAGS_RELEASE)
+                message(WARNING "CMAKE_C_FLAGS_RELEASE is not defined.")
+                set(CMAKE_C_FLAGS_RELEASE)
+            endif()
             if(MSVC)
                 string(REGEX REPLACE "[-|/]w " " " CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
                 string(REGEX REPLACE "[-|/]W[0|1|2|3|4|all|X] " " " CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
@@ -139,7 +147,7 @@ function(setup_project)
                     set(CMAKE_C_FLAGS_RELEASE ${CMAKE_C_FLAGS_RELEASE} PARENT_SCOPE)
                 endif()
             else()
-                string(REGEX REPLACE "-w " " " CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
+                string(REPLACE "-w " " " CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
                 string(REGEX REPLACE "-W[all|extra|error|pedantic] " " " CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
                 if(PROJ_ARGS_NO_WARNING)
                     string(APPEND CMAKE_C_FLAGS " -w ")
@@ -161,6 +169,14 @@ function(setup_project)
             set(CMAKE_CXX_STANDARD_REQUIRED ON PARENT_SCOPE)
             set(CMAKE_CXX_EXTENSIONS OFF PARENT_SCOPE)
             set(CMAKE_CXX_VISIBILITY_PRESET "hidden" PARENT_SCOPE)
+            if(NOT DEFINED CMAKE_CXX_FLAGS)
+                message(WARNING "CMAKE_CXX_FLAGS is not defined.")
+                set(CMAKE_CXX_FLAGS)
+            endif()
+            if(NOT DEFINED CMAKE_CXX_FLAGS_RELEASE)
+                message(WARNING "CMAKE_CXX_FLAGS_RELEASE is not defined.")
+                set(CMAKE_CXX_FLAGS_RELEASE)
+            endif()
             if(MSVC)
                 string(REGEX REPLACE "[-|/]GR-? " " " CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
                 string(REGEX REPLACE "[-|/]EH(a-?|r-?|s-?|c-?)+ " " " CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
@@ -193,7 +209,7 @@ function(setup_project)
                     set(CMAKE_CXX_FLAGS_RELEASE ${CMAKE_CXX_FLAGS_RELEASE} PARENT_SCOPE)
                 endif()
             else()
-                string(REGEX REPLACE "-w " " " CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
+                string(REPLACE "-w " " " CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
                 string(REGEX REPLACE "-W[all|extra|error|pedantic] " " " CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
                 if(PROJ_ARGS_NO_WARNING)
                     string(APPEND CMAKE_CXX_FLAGS " -w ")