Index: Modules/_io/fileio.c
===================================================================
--- Modules/_io/fileio.c	(révision 86919)
+++ Modules/_io/fileio.c	(copie de travail)
@@ -506,7 +506,7 @@
 fileio_readinto(fileio *self, PyObject *args)
 {
     Py_buffer pbuf;
-    Py_ssize_t n;
+    Py_ssize_t n, len;

     if (self->fd < 0)
         return err_closed();
@@ -517,9 +517,16 @@
         return NULL;

     if (_PyVerify_fd(self->fd)) {
+        len = pbuf.len;
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-        n = read(self->fd, pbuf.buf, pbuf.len);
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        if (len > INT_MAX)
+            len = INT_MAX;
+        n = read(self->fd, pbuf.buf, (int)len);
+#else
+        n = read(self->fd, pbuf.buf, (size_t)len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -685,7 +692,7 @@
 fileio_write(fileio *self, PyObject *args)
 {
     Py_buffer pbuf;
-    Py_ssize_t n;
+    Py_ssize_t n, len;

     if (self->fd < 0)
         return err_closed();
@@ -698,7 +705,14 @@
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
-        n = write(self->fd, pbuf.buf, pbuf.len);
+        len = pbuf.len;
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        if (len > INT_MAX)
+            len = INT_MAX;
+        n = write(self->fd, pbuf.buf, (int)len);
+#else
+        n = write(self->fd, pbuf.buf, (size_t)len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(révision 86919)
+++ Modules/posixmodule.c	(copie de travail)
@@ -5664,7 +5664,7 @@
 {
     Py_buffer pbuf;
     int fd;
-    Py_ssize_t size;
+    Py_ssize_t size, len;

     if (!PyArg_ParseTuple(args, "iy*:write", &fd, &pbuf))
         return NULL;
@@ -5672,8 +5672,15 @@
         PyBuffer_Release(&pbuf);
         return posix_error();
     }
+    len = pbuf.len;
     Py_BEGIN_ALLOW_THREADS
-    size = write(fd, pbuf.buf, (size_t)pbuf.len);
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (len > INT_MAX)
+        len = INT_MAX;
+    size = write(fd, pbuf.buf, (int)len);
+#else
+    size = write(fd, pbuf.buf, (size_t)len);
+#endif
     Py_END_ALLOW_THREADS
     PyBuffer_Release(&pbuf);
     if (size < 0)