diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index ebb2abcbf81..5d6d78d8bb4 100644
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -1422,10 +1422,13 @@ func (fd *FD) WriteMsgInet4(p []byte, oob []byte, sa *syscall.SockaddrInet4) (in
 	if o.rsa == nil {
 		o.rsa = new(syscall.RawSockaddrAny)
 	}
-	len := sockaddrInet4ToRaw(o.rsa, sa)
+	var nameLen int32
+	if sa != nil {
+		nameLen = sockaddrInet4ToRaw(o.rsa, sa)
+	}
 	msg := newWSAMsg(p, oob, 0)
 	msg.Name = (syscall.Pointer)(unsafe.Pointer(o.rsa))
-	msg.Namelen = len
+	msg.Namelen = nameLen
 	n, err := fd.execIO(o, func(o *operation) (qty uint32, err error) {
 		err = windows.WSASendMsg(fd.Sysfd, &msg, 0, nil, &o.o, nil)
 		return qty, err
@@ -1449,9 +1452,12 @@ func (fd *FD) WriteMsgInet6(p []byte, oob []byte, sa *syscall.SockaddrInet6) (in
 		o.rsa = new(syscall.RawSockaddrAny)
 	}
 	msg := newWSAMsg(p, oob, 0)
-	len := sockaddrInet6ToRaw(o.rsa, sa)
+	var nameLen int32
+	if sa != nil {
+		nameLen = sockaddrInet6ToRaw(o.rsa, sa)
+	}
 	msg.Name = (syscall.Pointer)(unsafe.Pointer(o.rsa))
-	msg.Namelen = len
+	msg.Namelen = nameLen
 	n, err := fd.execIO(o, func(o *operation) (qty uint32, err error) {
 		err = windows.WSASendMsg(fd.Sysfd, &msg, 0, nil, &o.o, nil)
 		return qty, err