diff --git a/Misc/NEWS b/Misc/NEWS
index 9d05fc0..38dff5b 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -9,6 +9,9 @@
 Core and Builtins
 -----------------
 
+- Issue #9611, #9015: FileIO.read(), FileIO.readinto(), FileIO.write() and
+  os.write() clamp the length to INT_MAX on Windows.
+
 - Issue #1195: my_fgets() now always clears errors before calling fgets(). Fix
   the following case: sys.stdin.read() stopped with CTRL+d (end of file),
   raw_input() interrupted by CTRL+c.
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 25a0c27..9f90448 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -474,7 +474,7 @@
 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();
@@ -485,9 +485,16 @@
         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, len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -620,6 +627,10 @@
         return fileio_readall(self);
     }
 
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+    if (size > INT_MAX)
+        size = INT_MAX;
+#endif
     bytes = PyBytes_FromStringAndSize(NULL, size);
     if (bytes == NULL)
         return NULL;
@@ -628,7 +639,11 @@
     if (_PyVerify_fd(self->fd)) {
         Py_BEGIN_ALLOW_THREADS
         errno = 0;
+#if defined(MS_WIN64) || defined(MS_WINDOWS)
+        n = read(self->fd, ptr, (int)size);
+#else
         n = read(self->fd, ptr, size);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
@@ -655,7 +670,7 @@
 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();
@@ -668,7 +683,14 @@
     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, len);
+#endif
         Py_END_ALLOW_THREADS
     } else
         n = -1;
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index fbd343b..8d6a72e 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -3903,7 +3903,7 @@
 #endif
     gid_t grouplist[MAX_GROUPS];
 
-    /* On MacOSX getgroups(2) can return more than MAX_GROUPS results 
+    /* On MacOSX getgroups(2) can return more than MAX_GROUPS results
      * This is a helper variable to store the intermediate result when
      * that happens.
      *
@@ -6648,7 +6648,7 @@
 {
     Py_buffer pbuf;
     int fd;
-    Py_ssize_t size;
+    Py_ssize_t size, len;
 
     if (!PyArg_ParseTuple(args, "is*:write", &fd, &pbuf))
         return NULL;
@@ -6656,8 +6656,15 @@
         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, len);
+#endif
     Py_END_ALLOW_THREADS
     PyBuffer_Release(&pbuf);
     if (size < 0)