diff --git a/src/net/ipsock_posix.go b/src/net/ipsock_posix.go
index 0910f63d48..e433e8a91c 100644
--- a/src/net/ipsock_posix.go
+++ b/src/net/ipsock_posix.go
@@ -9,6 +9,7 @@ package net
 import (
 	"context"
 	"internal/poll"
+	"net/netip"
 	"runtime"
 	"syscall"
 )
@@ -196,3 +197,32 @@ func ipToSockaddr(family int, ip IP, port int, zone string) (syscall.Sockaddr, e
 	}
 	return nil, &AddrError{Err: "invalid address family", Addr: ip.String()}
 }
+
+func addrPortToSockaddrInet4(ap netip.AddrPort) (syscall.SockaddrInet4, error) {
+	// ipToSockaddrInet4 has special handling here for zero length slices.
+	// We do not, because netip has no concept of a generic zero IP address.
+	addr := ap.Addr()
+	if !addr.Is4() {
+		return syscall.SockaddrInet4{}, &AddrError{Err: "non-IPv4 address", Addr: addr.String()}
+	}
+	sa := syscall.SockaddrInet4{
+		Addr: addr.As4(),
+		Port: int(ap.Port()),
+	}
+	return sa, nil
+}
+
+func addrPortToSockaddrInet6(ap netip.AddrPort) (syscall.SockaddrInet6, error) {
+	// ipToSockaddrInet6 has special handling here for zero length slices.
+	// We do not, because netip has no concept of a generic zero IP address.
+	addr := ap.Addr()
+	if !addr.Is6() {
+		return syscall.SockaddrInet6{}, &AddrError{Err: "non-IPv6 address", Addr: addr.String()}
+	}
+	sa := syscall.SockaddrInet6{
+		Addr:   addr.As16(),
+		Port:   int(ap.Port()),
+		ZoneId: uint32(zoneCache.index(addr.Zone())),
+	}
+	return sa, nil
+}
diff --git a/src/net/udpsock.go b/src/net/udpsock.go
index 8c97ca7537..0d563fd4f5 100644
--- a/src/net/udpsock.go
+++ b/src/net/udpsock.go
@@ -114,6 +114,13 @@ func UDPAddrFromAddrPort(addr netip.AddrPort) *UDPAddr {
 	}
 }
 
+// An addrPortUDPAddr is a netip.AddrPort-based UDP address that satisfies the Addr interface.
+type addrPortUDPAddr struct {
+	netip.AddrPort
+}
+
+func (addrPortUDPAddr) Network() string { return "udp" }
+
 // UDPConn is the implementation of the Conn and PacketConn interfaces
 // for UDP network connections.
 type UDPConn struct {
@@ -244,11 +251,14 @@ func (c *UDPConn) WriteMsgUDP(b, oob []byte, addr *UDPAddr) (n, oobn int, err er
 
 // WriteMsgUDPAddrPort is like WriteMsgUDP but takes a netip.AddrPort instead of a UDPAddr.
 func (c *UDPConn) WriteMsgUDPAddrPort(b, oob []byte, addr netip.AddrPort) (n, oobn int, err error) {
-	// TODO(bradfitz): make this efficient, making the internal net package
-	// type throughout be netip.Addr and only converting to the net.IP slice
-	// version at the edge. But for now (2021-10-20), this is a wrapper around
-	// the old way.
-	return c.WriteMsgUDP(b, oob, UDPAddrFromAddrPort(addr))
+	if !c.ok() {
+		return 0, 0, syscall.EINVAL
+	}
+	n, oobn, err = c.writeMsgAddrPort(b, oob, addr)
+	if err != nil {
+		err = &OpError{Op: "write", Net: c.fd.net, Source: c.fd.laddr, Addr: addrPortUDPAddr{addr}, Err: err}
+	}
+	return
 }
 
 func newUDPConn(fd *netFD) *UDPConn { return &UDPConn{conn{fd}} }
diff --git a/src/net/udpsock_plan9.go b/src/net/udpsock_plan9.go
index c18af2356d..ac5afa2281 100644
--- a/src/net/udpsock_plan9.go
+++ b/src/net/udpsock_plan9.go
@@ -57,6 +57,10 @@ func (c *UDPConn) writeMsg(b, oob []byte, addr *UDPAddr) (n, oobn int, err error
 	return 0, 0, syscall.EPLAN9
 }
 
+func (c *UDPConn) writeMsgAddrPort(b, oob []byte, addr netip.AddrPort) (n, oobn int, err error) {
+	return 0, 0, syscall.EPLAN9
+}
+
 func (sd *sysDialer) dialUDP(ctx context.Context, laddr, raddr *UDPAddr) (*UDPConn, error) {
 	fd, err := dialPlan9(ctx, sd.network, laddr, raddr)
 	if err != nil {
diff --git a/src/net/udpsock_posix.go b/src/net/udpsock_posix.go
index b20025140f..646687d148 100644
--- a/src/net/udpsock_posix.go
+++ b/src/net/udpsock_posix.go
@@ -123,6 +123,34 @@ func (c *UDPConn) writeMsg(b, oob []byte, addr *UDPAddr) (n, oobn int, err error
 	return c.fd.writeMsg(b, oob, sa)
 }
 
+func (c *UDPConn) writeMsgAddrPort(b, oob []byte, addr netip.AddrPort) (n, oobn int, err error) {
+	if c.fd.isConnected && addr.IsValid() {
+		return 0, 0, ErrWriteToConnected
+	}
+	if !c.fd.isConnected && !addr.IsValid() {
+		return 0, 0, errMissingAddress
+	}
+
+	switch c.fd.family {
+	case syscall.AF_INET:
+		sa, err := addrPortToSockaddrInet4(addr)
+		if err != nil {
+			return 0, 0, err
+		}
+		// TODO: Implement writeMsgInet4 to avoid allocation converting sa to an interface.
+		return c.fd.writeMsg(b, oob, &sa)
+	case syscall.AF_INET6:
+		sa, err := addrPortToSockaddrInet6(addr)
+		if err != nil {
+			return 0, 0, err
+		}
+		// TODO: Implement writeMsgInet6 to avoid allocation converting sa to an interface.
+		return c.fd.writeMsg(b, oob, &sa)
+	default:
+		return 0, 0, &AddrError{Err: "invalid address family", Addr: addr.Addr().String()}
+	}
+}
+
 func (sd *sysDialer) dialUDP(ctx context.Context, laddr, raddr *UDPAddr) (*UDPConn, error) {
 	fd, err := internetSocket(ctx, sd.network, laddr, raddr, syscall.SOCK_DGRAM, 0, "dial", sd.Dialer.Control)
 	if err != nil {