diff --git a/ci/diffs/20260502-tools-headers-Regenerate-stddef.h-to-fix-BPF-selftes.patch b/ci/diffs/20260502-tools-headers-Regenerate-stddef.h-to-fix-BPF-selftes.patch
new file mode 100644
index 00000000..f5ec7d31
--- /dev/null
+++ b/ci/diffs/20260502-tools-headers-Regenerate-stddef.h-to-fix-BPF-selftes.patch
@@ -0,0 +1,81 @@
+From 7b9f2a8d1761159b2ed87e2d0a162660555727a7 Mon Sep 17 00:00:00 2001
+From: Paul Chaignon <paul.chaignon@gmail.com>
+Date: Sat, 2 May 2026 12:12:40 +0200
+Subject: [PATCH] tools/headers: Regenerate stddef.h to fix BPF selftests
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+With commit dacbfc167808 ("crypto: af_alg - Annotate struct af_alg_iv
+with __counted_by"), two selftests, test_tag and crypto_sanity, now
+indirectly rely on the __counted_by macro. On systems with commit
+dacbfc167808 in the installed UAPI headers, the selftests build fails
+with:
+
+  In file included from tools/testing/selftests/bpf/prog_tests/crypto_sanity.c:7:
+  /usr/include/linux/if_alg.h:45:22: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘__counted_by’
+     45 |         __u8    iv[] __counted_by(ivlen);
+        |                      ^~~~~~~~~~~~
+
+This patch fixes it by regenerating stddef.h in tools/include using the
+instructions from commit a778f5d46b62 ("tools/headers: Pull in stddef.h
+to uapi to fix BPF selftests build in CI").
+
+Fixes: dacbfc167808 ("crypto: af_alg - Annotate struct af_alg_iv with __counted_by")
+Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
+Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
+---
+ tools/include/uapi/linux/stddef.h | 26 +++++++++++++++++++++++++-
+ 1 file changed, 25 insertions(+), 1 deletion(-)
+
+diff --git a/tools/include/uapi/linux/stddef.h b/tools/include/uapi/linux/stddef.h
+index c53cde425406..457498259494 100644
+--- a/tools/include/uapi/linux/stddef.h
++++ b/tools/include/uapi/linux/stddef.h
+@@ -3,7 +3,6 @@
+ #define _LINUX_STDDEF_H
+ 
+ 
+-
+ #ifndef __always_inline
+ #define __always_inline __inline__
+ #endif
+@@ -36,6 +35,11 @@
+ 		struct __struct_group_tag(TAG) { MEMBERS } ATTRS NAME; \
+ 	} ATTRS
+ 
++#ifdef __cplusplus
++/* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */
++#define __DECLARE_FLEX_ARRAY(T, member)	\
++	T member[0]
++#else
+ /**
+  * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+  *
+@@ -52,3 +56,23 @@
+ 		TYPE NAME[]; \
+ 	}
+ #endif
++
++#ifndef __counted_by
++#define __counted_by(m)
++#endif
++
++#ifndef __counted_by_le
++#define __counted_by_le(m)
++#endif
++
++#ifndef __counted_by_be
++#define __counted_by_be(m)
++#endif
++
++#ifndef __counted_by_ptr
++#define __counted_by_ptr(m)
++#endif
++
++#define __kernel_nonstring
++
++#endif /* _LINUX_STDDEF_H */
+-- 
+2.54.0
+