From a3bdd9da0866c61c8c532afeee584683adc1b890 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vicente=20Mataix=20Ferr=C3=A1ndiz?= <vmataix@altair.com>
Date: Fri, 9 Jan 2026 11:07:54 +0100
Subject: [PATCH 1/2] fix: Fixes compilation failure with MSVC 17.12 (v14.44)
 and C++20: '_BACKUP_ITERATOR_DEBUG_LEVEL' undeclared when including span
 header from STL.

---
 include/pybind11/pybind11.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index c457e149c1..72ba78bed5 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -9,6 +9,14 @@
 */
 
 #pragma once
+
+// See Issue #5956. This fixes compilation failure with MSVC 17.12 (v14.44) and C++20: '_BACKUP_ITERATOR_DEBUG_LEVEL' undeclared when including span header from STL.
+#if defined(_MSC_VER)
+#ifndef _BACKUP_ITERATOR_DEBUG_LEVEL
+#define _BACKUP_ITERATOR_DEBUG_LEVEL 0
+#endif
+#endif
+
 #include "detail/class.h"
 #include "detail/dynamic_raw_ptr_cast_if_possible.h"
 #include "detail/exception_translation.h"

From c450c85937b0c2987e4aa140ce1202b061765938 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Fri, 9 Jan 2026 10:15:07 +0000
Subject: [PATCH 2/2] style: pre-commit fixes

---
 include/pybind11/pybind11.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index 72ba78bed5..bc9c2dd1f8 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -10,11 +10,12 @@
 
 #pragma once
 
-// See Issue #5956. This fixes compilation failure with MSVC 17.12 (v14.44) and C++20: '_BACKUP_ITERATOR_DEBUG_LEVEL' undeclared when including span header from STL.
+// See Issue #5956. This fixes compilation failure with MSVC 17.12 (v14.44) and C++20:
+// '_BACKUP_ITERATOR_DEBUG_LEVEL' undeclared when including span header from STL.
 #if defined(_MSC_VER)
-#ifndef _BACKUP_ITERATOR_DEBUG_LEVEL
-#define _BACKUP_ITERATOR_DEBUG_LEVEL 0
-#endif
+#    ifndef _BACKUP_ITERATOR_DEBUG_LEVEL
+#        define _BACKUP_ITERATOR_DEBUG_LEVEL 0
+#    endif
 #endif
 
 #include "detail/class.h"