diff --git a/Doc/library/lzma.rst b/Doc/library/lzma.rst
index 4e6db15a74f..3941ec18d07 100644
--- a/Doc/library/lzma.rst
+++ b/Doc/library/lzma.rst
@@ -120,8 +120,16 @@ Compressing and decompressing data in memory
    ``9`` (inclusive), optionally OR-ed with the constant
    :const:`PRESET_EXTREME`. If neither *preset* nor *filters* are given, the
    default behavior is to use :const:`PRESET_DEFAULT` (preset level ``6``).
-   Higher presets produce smaller output, but make compression more CPU- and
-   memory-intensive, and also increase the memory required for decompression.
+   Higher presets produce smaller output, but make the compression process
+   slower.
+
+   .. note::
+
+      In addition to being more CPU-intensive, compression with higher presets
+      also requires much more memory (and produces output that needs more memory
+      to decompress). With preset ``9`` for example, the overhead for an
+      :class:`LZMACompressor` object can be as high as 800MiB. For this reason,
+      it is generally best to stick with the default preset.
 
    The *filters* argument (if provided) should be a filter chain specifier.
    See :ref:`filter-chain-specs` for details.
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index a7cee599102..b5c16ca5120 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -1248,6 +1248,13 @@ class GeneralModuleTests(unittest.TestCase):
         srv.listen(0)
         srv.close()
 
+    @unittest.skipUnless(support.IPV6_ENABLED, 'IPv6 required for this test.')
+    def test_flowinfo(self):
+        self.assertRaises(OverflowError, socket.getnameinfo,
+                          ('::1',0, 0xffffffff), 0)
+        with socket.socket(socket.AF_INET6, socket.SOCK_STREAM) as s:
+            self.assertRaises(OverflowError, s.bind, ('::1', 0, -10))
+
 
 @unittest.skipUnless(HAVE_SOCKET_CAN, 'SocketCan required for this test.')
 class BasicCANTest(unittest.TestCase):
diff --git a/Misc/ACKS b/Misc/ACKS
index 88b67e014e2..12f4b49d8a3 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -698,6 +698,7 @@ John Nagle
 Takahiro Nakayama
 Travers Naran
 Charles-François Natali
+Vilmos Nebehaj
 Fredrik Nehr
 Tony Nelson
 Trent Nelson
diff --git a/Misc/NEWS b/Misc/NEWS
index ba151e646cc..827aa4e32a9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -1744,6 +1744,9 @@ Tools/Demos
 Extension Modules
 -----------------
 
+- Issue #9975: socket: Fix incorrect use of flowinfo and scope_id. Patch by
+  Vilmos Nebehaj.
+
 - Issue #7777: socket: Add Reliable Datagram Sockets (PF_RDS) support.
 
 - Issue #13159: FileIO and BZ2Compressor/BZ2Decompressor now use a linear-time
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 04ef0dc1b8d..b2ab5e95417 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1095,10 +1095,10 @@ makesockaddr(SOCKET_T sockfd, struct sockaddr *addr, size_t addrlen, int proto)
         PyObject *ret = NULL;
         if (addrobj) {
             a = (struct sockaddr_in6 *)addr;
-            ret = Py_BuildValue("Oiii",
+            ret = Py_BuildValue("OiII",
                                 addrobj,
                                 ntohs(a->sin6_port),
-                                a->sin6_flowinfo,
+                                ntohl(a->sin6_flowinfo),
                                 a->sin6_scope_id);
             Py_DECREF(addrobj);
         }
@@ -1386,7 +1386,8 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
     {
         struct sockaddr_in6* addr;
         char *host;
-        int port, flowinfo, scope_id, result;
+        int port, result;
+        unsigned int flowinfo, scope_id;
         flowinfo = scope_id = 0;
         if (!PyTuple_Check(args)) {
             PyErr_Format(
@@ -1396,7 +1397,7 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
                 Py_TYPE(args)->tp_name);
             return 0;
         }
-        if (!PyArg_ParseTuple(args, "eti|ii",
+        if (!PyArg_ParseTuple(args, "eti|II",
                               "idna", &host, &port, &flowinfo,
                               &scope_id)) {
             return 0;
@@ -1413,9 +1414,15 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
                 "getsockaddrarg: port must be 0-65535.");
             return 0;
         }
+        if (flowinfo < 0 || flowinfo > 0xfffff) {
+            PyErr_SetString(
+                PyExc_OverflowError,
+                "getsockaddrarg: flowinfo must be 0-1048575.");
+            return 0;
+        }
         addr->sin6_family = s->sock_family;
         addr->sin6_port = htons((short)port);
-        addr->sin6_flowinfo = flowinfo;
+        addr->sin6_flowinfo = htonl(flowinfo);
         addr->sin6_scope_id = scope_id;
         *len_ret = sizeof *addr;
         return 1;
@@ -4939,7 +4946,8 @@ socket_getnameinfo(PyObject *self, PyObject *args)
     PyObject *sa = (PyObject *)NULL;
     int flags;
     char *hostp;
-    int port, flowinfo, scope_id;
+    int port;
+    unsigned int flowinfo, scope_id;
     char hbuf[NI_MAXHOST], pbuf[NI_MAXSERV];
     struct addrinfo hints, *res = NULL;
     int error;
@@ -4953,9 +4961,14 @@ socket_getnameinfo(PyObject *self, PyObject *args)
                         "getnameinfo() argument 1 must be a tuple");
         return NULL;
     }
-    if (!PyArg_ParseTuple(sa, "si|ii",
+    if (!PyArg_ParseTuple(sa, "si|II",
                           &hostp, &port, &flowinfo, &scope_id))
         return NULL;
+    if (flowinfo < 0 || flowinfo > 0xfffff) {
+        PyErr_SetString(PyExc_OverflowError,
+                        "getsockaddrarg: flowinfo must be 0-1048575.");
+        return NULL;
+    }
     PyOS_snprintf(pbuf, sizeof(pbuf), "%d", port);
     memset(&hints, 0, sizeof(hints));
     hints.ai_family = AF_UNSPEC;
@@ -4990,7 +5003,7 @@ socket_getnameinfo(PyObject *self, PyObject *args)
         {
         struct sockaddr_in6 *sin6;
         sin6 = (struct sockaddr_in6 *)res->ai_addr;
-        sin6->sin6_flowinfo = flowinfo;
+        sin6->sin6_flowinfo = htonl(flowinfo);
         sin6->sin6_scope_id = scope_id;
         break;
         }