diff --git a/.github/workflows/root-ci.yml b/.github/workflows/root-ci.yml
index 029e4de73c02d..86587dae53c81 100644
--- a/.github/workflows/root-ci.yml
+++ b/.github/workflows/root-ci.yml
@@ -412,7 +412,7 @@ jobs:
           - image: alma10
             is_special: true
             property: "clang Ninja"
-            overrides: ["CMAKE_C_COMPILER=clang", "CMAKE_CXX_COMPILER=clang++"]
+            overrides: ["CMAKE_C_COMPILER=clang", "CMAKE_CXX_COMPILER=clang++", "CMAKE_CXX_STANDARD=23", "libcxx=ON"]
             cmake_generator: Ninja
           # Fedora Rawhide with Python debug build
           - image: rawhide
diff --git a/cmake/modules/SearchInstalledSoftware.cmake b/cmake/modules/SearchInstalledSoftware.cmake
index b55accf14b143..d672894e96c68 100644
--- a/cmake/modules/SearchInstalledSoftware.cmake
+++ b/cmake/modules/SearchInstalledSoftware.cmake
@@ -2211,7 +2211,7 @@ if(NOT ROOT_HAVE_NATIVE_CXX_FILESYSTEM)
   set(CMAKE_REQUIRED_LIBRARIES stdc++fs)
   check_cxx_source_compiles("${_filesystem_source}" ROOT_NEED_STDCXXFS)
   if(NOT ROOT_NEED_STDCXXFS)
-    message(FATAL_ERROR "Could not determine how to use C++17 <filesystem>")
+    message(WARNING "Could not determine how to use C++17 <filesystem>")
   endif()
 endif()