diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 84d31cb1e..cf46e99d0 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -32,7 +32,7 @@ repos:
     exclude: ^noxfile.py$
 
 - repo: https://github.com/asottile/pyupgrade
-  rev: v2.21.2
+  rev: v2.23.0
   hooks:
   - id: pyupgrade
 
diff --git a/include/pybind11/buffer_info.h b/include/pybind11/buffer_info.h
index 47dc39d4e..eba68d1aa 100644
--- a/include/pybind11/buffer_info.h
+++ b/include/pybind11/buffer_info.h
@@ -83,7 +83,7 @@ struct buffer_info {
             view->strides
             ? std::vector<ssize_t>(view->strides, view->strides + view->ndim)
             : detail::c_strides({view->shape, view->shape + view->ndim}, view->itemsize),
-            view->readonly) {
+            (view->readonly != 0)) {
         this->m_view = view;
         this->ownview = ownview;
     }
diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index c7787cd8a..7cf246a62 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -344,7 +344,7 @@ public:
             }
             #endif
             if (res == 0 || res == 1) {
-                value = (bool) res;
+                value = (res != 0);
                 return true;
             }
             PyErr_Clear();
diff --git a/include/pybind11/chrono.h b/include/pybind11/chrono.h
index d32b5b056..c4e81f572 100644
--- a/include/pybind11/chrono.h
+++ b/include/pybind11/chrono.h
@@ -11,9 +11,14 @@
 #pragma once
 
 #include "pybind11.h"
+
+#include <chrono>
 #include <cmath>
 #include <ctime>
-#include <chrono>
+#include <mutex>
+
+#include <time.h>
+
 #include <datetime.h>
 
 // Backport the PyDateTime_DELTA functions from Python3.3 if required
@@ -95,6 +100,22 @@ public:
     PYBIND11_TYPE_CASTER(type, _("datetime.timedelta"));
 };
 
+inline std::tm *localtime_thread_safe(const std::time_t *time, std::tm *buf) {
+#if defined(__STDC_WANT_LIB_EXT1__) || defined(_MSC_VER)
+    if (localtime_s(buf, time))
+        return nullptr;
+    return buf;
+#else
+    static std::mutex mtx;
+    std::lock_guard<std::mutex> lock(mtx);
+    std::tm *tm_ptr = localtime(time);
+    if (tm_ptr != nullptr) {
+        *buf = *tm_ptr;
+    }
+    return tm_ptr;
+#endif
+}
+
 // This is for casting times on the system clock into datetime.datetime instances
 template <typename Duration> class type_caster<std::chrono::time_point<std::chrono::system_clock, Duration>> {
 public:
@@ -162,16 +183,10 @@ public:
         // (https://en.cppreference.com/w/cpp/chrono/system_clock/to_time_t)
         std::time_t tt = system_clock::to_time_t(time_point_cast<system_clock::duration>(src - us));
 
-        // std::localtime returns a pointer to a static internal std::tm object on success,
-        // or null pointer otherwise
-        std::tm *localtime_ptr = std::localtime(&tt);
+        std::tm localtime;
+        std::tm *localtime_ptr = localtime_thread_safe(&tt, &localtime);
         if (!localtime_ptr)
             throw cast_error("Unable to represent system_clock in local time");
-
-        // this function uses static memory so it's best to copy it out asap just in case
-        // otherwise other code that is using localtime may break this (not just python code)
-        std::tm localtime = *localtime_ptr;
-
         return PyDateTime_FromDateAndTime(localtime.tm_year + 1900,
                                           localtime.tm_mon + 1,
                                           localtime.tm_mday,
diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index 52b019335..3faf3ea32 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -125,6 +125,11 @@
 #  endif
 #endif
 
+// https://en.cppreference.com/w/c/chrono/localtime
+#if defined(__STDC_LIB_EXT1__) && !defined(__STDC_WANT_LIB_EXT1__)
+#    define __STDC_WANT_LIB_EXT1__
+#endif
+
 #include <Python.h>
 #include <frameobject.h>
 #include <pythread.h>
diff --git a/include/pybind11/detail/pragma_warning_block.h b/include/pybind11/detail/pragma_warning_block.h
index 9046e2828..b774c549c 100644
--- a/include/pybind11/detail/pragma_warning_block.h
+++ b/include/pybind11/detail/pragma_warning_block.h
@@ -8,9 +8,6 @@
 #  pragma warning(push)
 #  pragma warning(disable: 4100) // warning C4100: Unreferenced formal parameter
 #  pragma warning(disable: 4127) // warning C4127: Conditional expression is constant
-#  pragma warning(disable: 4800) // warning C4800: 'int': forcing value to bool 'true' or 'false' (performance warning)
-#  pragma warning(disable: 4996) // warning C4996: The POSIX name for this item is deprecated. Instead, use the ISO C and C++ conformant name
-#  pragma warning(disable: 4522) // warning C4522: multiple assignment operators specified
 #  pragma warning(disable: 4505) // warning C4505: 'PySlice_GetIndicesEx': unreferenced local function has been removed (PyPy only)
 #elif defined(__GNUG__) && !defined(__clang__)
 #  pragma GCC diagnostic push
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index bdf3a3982..a6b6bea6a 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -231,7 +231,7 @@ struct value_and_holder {
         return reinterpret_cast<V *&>(vh[0]);
     }
     // True if this `value_and_holder` has a non-null value pointer
-    explicit operator bool() const { return value_ptr(); }
+    explicit operator bool() const { return value_ptr() != nullptr; }
 
     template <typename H> H &holder() const {
         return reinterpret_cast<H &>(vh[1]);
@@ -252,7 +252,7 @@ struct value_and_holder {
     bool instance_registered() const {
         return inst->simple_layout
             ? inst->simple_instance_registered
-            : inst->nonsimple.status[index] & instance::status_instance_registered;
+            : ((inst->nonsimple.status[index] & instance::status_instance_registered) != 0);
     }
     void set_instance_registered(bool v = true) const {
         if (inst->simple_layout)
diff --git a/include/pybind11/pybind11.h b/include/pybind11/pybind11.h
index c59713d93..1dbd3d959 100644
--- a/include/pybind11/pybind11.h
+++ b/include/pybind11/pybind11.h
@@ -28,6 +28,8 @@
 #include <string>
 #include <utility>
 
+#include <string.h>
+
 #if defined(__cpp_lib_launder) && !(defined(_MSC_VER) && (_MSC_VER < 1914))
 #  define PYBIND11_STD_LAUNDER std::launder
 #  define PYBIND11_HAS_STD_LAUNDER 1
@@ -61,8 +63,13 @@ inline bool apply_exception_translators(std::forward_list<ExceptionTranslator>&
     return false;
 }
 
-PYBIND11_NAMESPACE_END(detail)
+#if defined(_MSC_VER)
+#    define PYBIND11_COMPAT_STRDUP _strdup
+#else
+#    define PYBIND11_COMPAT_STRDUP strdup
+#endif
 
+PYBIND11_NAMESPACE_END(detail)
 
 /// Wraps an arbitrary C++ function/method/lambda function/.. into a callable Python object
 class cpp_function : public function {
@@ -261,7 +268,7 @@ protected:
                 std::free(s);
         }
         char *operator()(const char *s) {
-            auto t = strdup(s);
+            auto t = PYBIND11_COMPAT_STRDUP(s);
             strings.push_back(t);
             return t;
         }
@@ -505,7 +512,8 @@ protected:
         auto *func = (PyCFunctionObject *) m_ptr;
         std::free(const_cast<char *>(func->m_ml->ml_doc));
         // Install docstring if it's non-empty (when at least one option is enabled)
-        func->m_ml->ml_doc = signatures.empty() ? nullptr : strdup(signatures.c_str());
+        func->m_ml->ml_doc
+            = signatures.empty() ? nullptr : PYBIND11_COMPAT_STRDUP(signatures.c_str());
 
         if (rec->is_method) {
             m_ptr = PYBIND11_INSTANCE_METHOD_NEW(m_ptr, rec->scope.ptr());
@@ -1596,7 +1604,7 @@ public:
            detail::process_attributes<Extra...>::init(extra..., rec_fget);
            if (rec_fget->doc && rec_fget->doc != doc_prev) {
               free(doc_prev);
-              rec_fget->doc = strdup(rec_fget->doc);
+              rec_fget->doc = PYBIND11_COMPAT_STRDUP(rec_fget->doc);
            }
         }
         if (rec_fset) {
@@ -1604,7 +1612,7 @@ public:
             detail::process_attributes<Extra...>::init(extra..., rec_fset);
             if (rec_fset->doc && rec_fset->doc != doc_prev) {
                 free(doc_prev);
-                rec_fset->doc = strdup(rec_fset->doc);
+                rec_fset->doc = PYBIND11_COMPAT_STRDUP(rec_fset->doc);
             }
             if (! rec_active) rec_active = rec_fset;
         }
diff --git a/include/pybind11/pytypes.h b/include/pybind11/pytypes.h
index b483fb323..cea4e7eb0 100644
--- a/include/pybind11/pytypes.h
+++ b/include/pybind11/pytypes.h
@@ -367,7 +367,9 @@ public:
     /// Check if the currently trapped error type matches the given Python exception class (or a
     /// subclass thereof).  May also be passed a tuple to search for any exception class matches in
     /// the given tuple.
-    bool matches(handle exc) const { return PyErr_GivenExceptionMatches(m_type.ptr(), exc.ptr()); }
+    bool matches(handle exc) const {
+        return (PyErr_GivenExceptionMatches(m_type.ptr(), exc.ptr()) != 0);
+    }
 
     const object& type() const { return m_type; }
     const object& value() const { return m_value; }
@@ -532,6 +534,10 @@ object object_or_cast(T &&o);
 // Match a PyObject*, which we want to convert directly to handle via its converting constructor
 inline handle object_or_cast(PyObject *ptr) { return ptr; }
 
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#  pragma warning(push)
+#  pragma warning(disable: 4522) // warning C4522: multiple assignment operators specified
+#endif
 template <typename Policy>
 class accessor : public object_api<accessor<Policy>> {
     using key_type = typename Policy::key_type;
@@ -580,6 +586,9 @@ private:
     key_type key;
     mutable object cache;
 };
+#if defined(_MSC_VER) && _MSC_VER < 1920
+#  pragma warning(pop)
+#endif
 
 PYBIND11_NAMESPACE_BEGIN(accessor_policies)
 struct obj_attr {
@@ -846,7 +855,7 @@ PYBIND11_NAMESPACE_END(detail)
         Name(handle h, borrowed_t) : Parent(h, borrowed_t{}) { } \
         Name(handle h, stolen_t) : Parent(h, stolen_t{}) { } \
         PYBIND11_DEPRECATED("Use py::isinstance<py::python_type>(obj) instead") \
-        bool check() const { return m_ptr != nullptr && (bool) CheckFun(m_ptr); } \
+        bool check() const { return m_ptr != nullptr && (CheckFun(m_ptr) != 0); } \
         static bool check_(handle h) { return h.ptr() != nullptr && CheckFun(h.ptr()); } \
         template <typename Policy_> \
         Name(const ::pybind11::detail::accessor<Policy_> &a) : Name(object(a)) { }