diff --git a/contrib/buildsystems/CMakeLists.txt b/contrib/buildsystems/CMakeLists.txt
index e76bd19b65..7874e5a326 100644
--- a/contrib/buildsystems/CMakeLists.txt
+++ b/contrib/buildsystems/CMakeLists.txt
@@ -258,7 +258,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Windows")
 				OVERRIDE_STRDUP MMAP_PREVENTS_DELETE USE_WIN32_MMAP
 				HAVE_WPGMPTR HAVE_RTLGENRANDOM)
 	if(CMAKE_GENERATOR_PLATFORM STREQUAL "x64")
-		add_compile_definitions(ENSURE_MSYSTEM_IS_SET="MINGW64" MINGW_PREFIX="mingw64")
+		add_compile_definitions(ENSURE_MSYSTEM_IS_SET="UCRT64" MINGW_PREFIX="ucrt64")
 	elseif(CMAKE_GENERATOR_PLATFORM STREQUAL "arm64")
 		add_compile_definitions(ENSURE_MSYSTEM_IS_SET="CLANGARM64" MINGW_PREFIX="clangarm64")
 	elseif(CMAKE_GENERATOR_PLATFORM STREQUAL "x86")