diff --git a/cmake/GNUWarnings.cmake b/cmake/GNUWarnings.cmake
index 62362ed2..252927a6 100644
--- a/cmake/GNUWarnings.cmake
+++ b/cmake/GNUWarnings.cmake
@@ -71,7 +71,7 @@ function(_gw_check_c_flag_is_silent FLAG)
     file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.c" "")
     _gw_check_command_succeeds_silently(_result "${CMAKE_C_COMPILER}" "${FLAG}" "-c" "-o" "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.o" "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.c")
     message(STATUS "Have C warning ${flag}: ${_result}")
-    set("GNUWARNINGS_C_FLAG_${FLAG}_SILENT" "${_result}" CACHE BOOL "Have C warning ${flag}")
+    set("GNUWARNINGS_C_FLAG_${FLAG}_SILENT" "${_result}" CACHE INTERNAL "Have C warning ${flag}")
   endif()
 endfunction()
 
@@ -80,7 +80,7 @@ function(_gw_check_cxx_flag_is_silent FLAG)
     file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.cpp" "")
     _gw_check_command_succeeds_silently(_result "${CMAKE_CXX_COMPILER}" "${FLAG}" "-c" "-o" "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.o" "${CMAKE_CURRENT_BINARY_DIR}/CheckGNUWarning.cpp")
     message(STATUS "Have C++ warning ${flag}: ${_result}")
-    set("GNUWARNINGS_CXX_FLAG_${FLAG}_SILENT" "${_result}" CACHE BOOL "Have C++ warning ${flag}")
+    set("GNUWARNINGS_CXX_FLAG_${FLAG}_SILENT" "${_result}" CACHE INTERNAL "Have C++ warning ${flag}")
   endif()
 endfunction()