diff --git a/cmake/setup_compiler_flags_gnu.cmake b/cmake/setup_compiler_flags_gnu.cmake
index a352c9839295..0847db4316d7 100644
--- a/cmake/setup_compiler_flags_gnu.cmake
+++ b/cmake/setup_compiler_flags_gnu.cmake
@@ -192,7 +192,10 @@ if (CMAKE_BUILD_TYPE MATCHES "Debug")
   # Enable invalid element access and other checks in the c++ standard libray:
   list(APPEND DEAL_II_DEFINITIONS_DEBUG "_GLIBCXX_ASSERTIONS")
   if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    list(APPEND DEAL_II_DEFINITIONS_DEBUG "_LIBCPP_ENABLE_ASSERTIONS")
+    if (CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19)
+      # _LIBCPP_ENABLE_ASSERTIONS was deprecated in clang++-19
+      list(APPEND DEAL_II_DEFINITIONS_DEBUG "_LIBCPP_ENABLE_ASSERTIONS")
+    endif()
     list(APPEND DEAL_II_DEFINITIONS_DEBUG "_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE")
   endif()