diff --git a/sys-devel/llvm/patches/llvm21-21.1.0.patchset b/sys-devel/llvm/patches/llvm21-21.1.0.patchset
index b4ac0e863..70b5077ad 100644
--- a/sys-devel/llvm/patches/llvm21-21.1.0.patchset
+++ b/sys-devel/llvm/patches/llvm21-21.1.0.patchset
@@ -426,3 +426,25 @@ index 945076e..821fc1a 100644
 -- 
 2.48.1
 
+
+From 57b350100356031511f7b454485d57b47c09e72e Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Duval?= <jerome.duval@gmail.com>
+Date: Sun, 31 Aug 2025 13:24:42 +0200
+Subject: sanitizer_linux_libcdep.cpp: current bot version needs _GNU_SOURCE
+
+
+diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+index f5cb85b..530ff90 100644
+--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
++++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+@@ -29,6 +29,7 @@
+ #  include "sanitizer_solaris.h"
+ 
+ #  if SANITIZER_HAIKU
++#    define _GNU_SOURCE
+ #    define _DEFAULT_SOURCE
+ #  endif
+ 
+-- 
+2.48.1
+