diff --git a/go.mod b/go.mod
index 66328a7..75b14dd 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,7 @@
 go 1.11
 
 require (
-	golang.org/x/sys v0.0.0-20201119102817-f84b799fce68
+	golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005
 	golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1
 	golang.org/x/text v0.3.3
 )
diff --git a/go.sum b/go.sum
index 7c94510..3c5bdb0 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,6 @@
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68 h1:nxC68pudNYkKU6jWhgrqdreuFiOQWj1Fs7T3VrH4Pjw=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005 h1:pDMpM2zh2MT0kHy037cKlSby2nEhD50SYqwQk76Nm40=
+golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 h1:v+OssWQX+hTHEmOBgwxdZxK4zHq3yOs8F9J7mk0PY8E=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
diff --git a/http2/h2demo/go.sum b/http2/h2demo/go.sum
index d00ad9c..2e481df 100644
--- a/http2/h2demo/go.sum
+++ b/http2/h2demo/go.sum
@@ -14,12 +14,10 @@
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/mock v1.2.0/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
-github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
 github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.3.1 h1:YF8+flBXS5eO826T4nzqPrxfhQThhXl0YzfuUPu4SBg=
 github.com/golang/protobuf v1.3.1/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
-github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
 github.com/google/go-cmp v0.3.0 h1:crn/baboCvb5fXaQ0IJ1SGTsTVrWpDsCWC8EGETZijY=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
@@ -45,7 +43,6 @@
 go4.org v0.0.0-20190218023631-ce4c26f7be8e/go.mod h1:MkTOUMDaeVYJUOUsaDXIhWPZYa1yOyC1qaOBpL57BhE=
 golang.org/x/build v0.0.0-20190509182522-45de920fc22c h1:lgCiAYQNZHWRJOB1au5nVtnBZS1ZmKN1DpViRg23ZZc=
 golang.org/x/build v0.0.0-20190509182522-45de920fc22c/go.mod h1:fYw7AShPAhGMdXqA9gRadk/CcMsvLlClpE5oBwnS3dM=
-golang.org/x/crypto v0.0.0-20190424203555-c05e17bb3b2d h1:adrbvkTDn9rGnXg2IJDKozEpXXLZN89pdIA+Syt4/u0=
 golang.org/x/crypto v0.0.0-20190424203555-c05e17bb3b2d/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9 h1:psW17arqaxU48Z5kZ0CQnkZWQJsqcURM6tKiBApRjXI=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
@@ -60,24 +57,20 @@
 golang.org/x/oauth2 v0.0.0-20190402181905-9f3314589c9a/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/perf v0.0.0-20180704124530-6e6d33e29852/go.mod h1:JLpeXjPJfIyPr5TlbXLkXWLhP8nz10XfvxElABhCtcw=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
-golang.org/x/sync v0.0.0-20181108010431-42b317875d0f h1:Bl/8QSvNqXvPGPGXa2z5xUTmV7VDcZyvRZ+QQXkXTZQ=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190227155943-e225da77a7e6/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a h1:1BGLXjeY4akVXGgbC9HugT3Jv3hCI0z56oJR5vAMgBU=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20190502175342-a43fa875dd82 h1:vsphBvatvfbhlb4PO1BYSr9dzugGxJ/SQHoNufZJq1w=
 golang.org/x/sys v0.0.0-20190502175342-a43fa875dd82/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20201119102817-f84b799fce68 h1:nxC68pudNYkKU6jWhgrqdreuFiOQWj1Fs7T3VrH4Pjw=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005 h1:pDMpM2zh2MT0kHy037cKlSby2nEhD50SYqwQk76Nm40=
+golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2 h1:z99zHgr7hKfrUcX/KsoJk5FJfjTceCKIp96+biqP4To=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/text v0.3.3 h1:cokOdA+Jmi5PJGXLlLllQSgYigAEfHXJAERHVMaCc2k=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
diff --git a/ipv4/sys_windows.go b/ipv4/sys_windows.go
index 955f7f4..c5e9506 100644
--- a/ipv4/sys_windows.go
+++ b/ipv4/sys_windows.go
@@ -7,24 +7,11 @@
 import (
 	"golang.org/x/net/internal/iana"
 	"golang.org/x/net/internal/socket"
+
+	"golang.org/x/sys/windows"
 )
 
 const (
-	// See ws2tcpip.h.
-	sysIP_OPTIONS                = 0x1
-	sysIP_HDRINCL                = 0x2
-	sysIP_TOS                    = 0x3
-	sysIP_TTL                    = 0x4
-	sysIP_MULTICAST_IF           = 0x9
-	sysIP_MULTICAST_TTL          = 0xa
-	sysIP_MULTICAST_LOOP         = 0xb
-	sysIP_ADD_MEMBERSHIP         = 0xc
-	sysIP_DROP_MEMBERSHIP        = 0xd
-	sysIP_DONTFRAGMENT           = 0xe
-	sysIP_ADD_SOURCE_MEMBERSHIP  = 0xf
-	sysIP_DROP_SOURCE_MEMBERSHIP = 0x10
-	sysIP_PKTINFO                = 0x13
-
 	sizeofIPMreq       = 0x8
 	sizeofIPMreqSource = 0xc
 )
@@ -45,13 +32,13 @@
 	ctlOpts = [ctlMax]ctlOpt{}
 
 	sockOpts = map[int]*sockOpt{
-		ssoTOS:                {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_TOS, Len: 4}},
-		ssoTTL:                {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_TTL, Len: 4}},
-		ssoMulticastTTL:       {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_MULTICAST_TTL, Len: 4}},
-		ssoMulticastInterface: {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_MULTICAST_IF, Len: 4}},
-		ssoMulticastLoopback:  {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_MULTICAST_LOOP, Len: 4}},
-		ssoHeaderPrepend:      {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_HDRINCL, Len: 4}},
-		ssoJoinGroup:          {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_ADD_MEMBERSHIP, Len: sizeofIPMreq}, typ: ssoTypeIPMreq},
-		ssoLeaveGroup:         {Option: socket.Option{Level: iana.ProtocolIP, Name: sysIP_DROP_MEMBERSHIP, Len: sizeofIPMreq}, typ: ssoTypeIPMreq},
+		ssoTOS:                {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_TOS, Len: 4}},
+		ssoTTL:                {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_TTL, Len: 4}},
+		ssoMulticastTTL:       {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_MULTICAST_TTL, Len: 4}},
+		ssoMulticastInterface: {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_MULTICAST_IF, Len: 4}},
+		ssoMulticastLoopback:  {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_MULTICAST_LOOP, Len: 4}},
+		ssoHeaderPrepend:      {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_HDRINCL, Len: 4}},
+		ssoJoinGroup:          {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_ADD_MEMBERSHIP, Len: sizeofIPMreq}, typ: ssoTypeIPMreq},
+		ssoLeaveGroup:         {Option: socket.Option{Level: iana.ProtocolIP, Name: windows.IP_DROP_MEMBERSHIP, Len: sizeofIPMreq}, typ: ssoTypeIPMreq},
 	}
 )
diff --git a/ipv6/sys_windows.go b/ipv6/sys_windows.go
index fc36b01..fda8a29 100644
--- a/ipv6/sys_windows.go
+++ b/ipv6/sys_windows.go
@@ -10,18 +10,11 @@
 
 	"golang.org/x/net/internal/iana"
 	"golang.org/x/net/internal/socket"
+
+	"golang.org/x/sys/windows"
 )
 
 const (
-	// See ws2tcpip.h.
-	sysIPV6_UNICAST_HOPS   = 0x4
-	sysIPV6_MULTICAST_IF   = 0x9
-	sysIPV6_MULTICAST_HOPS = 0xa
-	sysIPV6_MULTICAST_LOOP = 0xb
-	sysIPV6_JOIN_GROUP     = 0xc
-	sysIPV6_LEAVE_GROUP    = 0xd
-	sysIPV6_PKTINFO        = 0x13
-
 	sizeofSockaddrInet6 = 0x1c
 
 	sizeofIPv6Mreq     = 0x14
@@ -55,12 +48,12 @@
 	ctlOpts = [ctlMax]ctlOpt{}
 
 	sockOpts = map[int]*sockOpt{
-		ssoHopLimit:           {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_UNICAST_HOPS, Len: 4}},
-		ssoMulticastInterface: {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_MULTICAST_IF, Len: 4}},
-		ssoMulticastHopLimit:  {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_MULTICAST_HOPS, Len: 4}},
-		ssoMulticastLoopback:  {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_MULTICAST_LOOP, Len: 4}},
-		ssoJoinGroup:          {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_JOIN_GROUP, Len: sizeofIPv6Mreq}, typ: ssoTypeIPMreq},
-		ssoLeaveGroup:         {Option: socket.Option{Level: iana.ProtocolIPv6, Name: sysIPV6_LEAVE_GROUP, Len: sizeofIPv6Mreq}, typ: ssoTypeIPMreq},
+		ssoHopLimit:           {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_UNICAST_HOPS, Len: 4}},
+		ssoMulticastInterface: {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_MULTICAST_IF, Len: 4}},
+		ssoMulticastHopLimit:  {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_MULTICAST_HOPS, Len: 4}},
+		ssoMulticastLoopback:  {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_MULTICAST_LOOP, Len: 4}},
+		ssoJoinGroup:          {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_JOIN_GROUP, Len: sizeofIPv6Mreq}, typ: ssoTypeIPMreq},
+		ssoLeaveGroup:         {Option: socket.Option{Level: iana.ProtocolIPv6, Name: windows.IPV6_LEAVE_GROUP, Len: sizeofIPv6Mreq}, typ: ssoTypeIPMreq},
 	}
 )