diff --git a/cmake/xo_cxx.cmake b/cmake/xo_cxx.cmake
index c7f163d2..b02ad99a 100644
--- a/cmake/xo_cxx.cmake
+++ b/cmake/xo_cxx.cmake
@@ -1,5 +1,12 @@
 
 macro(xo_toplevel_compile_options)
+    if(NOT DEFINED CMAKE_CXX_STANDARD)
+        set(CMAKE_CXX_STANDARD 20)
+    endif()
+    if(NOT DEFINED CMAKE_CXX_STANDARD_REQUIRED)
+        set(CMAKE_CXX_STANDARD_REQUIRED True)
+    endif()
+
     # ----------------------------------------------------------------
     # variable
     #   XO_ADDRESS_SANITIZE