diff --git a/src/internal/poll/sendfile.go b/src/internal/poll/sendfile.go
index 41b0481c1a..696d93353e 100644
--- a/src/internal/poll/sendfile.go
+++ b/src/internal/poll/sendfile.go
@@ -4,4 +4,4 @@
 
 package poll
 
-var TestHookDidSendFile = func(dstFD *FD, src int, written int64, err error, handled bool) {}
+var TestHookDidSendFile = func(dstFD *FD, src uintptr, written int64, err error, handled bool) {}
diff --git a/src/internal/poll/sendfile_unix.go b/src/internal/poll/sendfile_unix.go
index 1105e05691..4b7e9fea9e 100644
--- a/src/internal/poll/sendfile_unix.go
+++ b/src/internal/poll/sendfile_unix.go
@@ -27,29 +27,29 @@ import (
 // If handled is false, sendfile was unable to perform the copy,
 // has not modified the source or destination,
 // and the caller should perform the copy using a fallback implementation.
-func SendFile(dstFD *FD, src int, size int64) (n int64, err error, handled bool) {
+func SendFile(dstFD *FD, src uintptr, size int64) (n int64, err error, handled bool) {
 	if goos := runtime.GOOS; goos == "linux" || goos == "android" {
 		// Linux's sendfile doesn't require any setup:
 		// It sends from the current position of the source file and
 		// updates the position of the source after sending.
-		return sendFile(dstFD, src, nil, size)
+		return sendFile(dstFD, int(src), nil, size)
 	}
 
 	// Non-Linux sendfile implementations don't use the current position of the source file,
 	// so we need to look up the position, pass it explicitly, and adjust it after
 	// sendfile returns.
 	start, err := ignoringEINTR2(func() (int64, error) {
-		return syscall.Seek(src, 0, io.SeekCurrent)
+		return syscall.Seek(int(src), 0, io.SeekCurrent)
 	})
 	if err != nil {
 		return 0, err, false
 	}
 
 	pos := start
-	n, err, handled = sendFile(dstFD, src, &pos, size)
+	n, err, handled = sendFile(dstFD, int(src), &pos, size)
 	if n > 0 {
 		ignoringEINTR2(func() (int64, error) {
-			return syscall.Seek(src, start+n, io.SeekStart)
+			return syscall.Seek(int(src), start+n, io.SeekStart)
 		})
 	}
 	return n, err, handled
@@ -58,7 +58,7 @@ func SendFile(dstFD *FD, src int, size int64) (n int64, err error, handled bool)
 // sendFile wraps the sendfile system call.
 func sendFile(dstFD *FD, src int, offset *int64, size int64) (written int64, err error, handled bool) {
 	defer func() {
-		TestHookDidSendFile(dstFD, src, written, err, handled)
+		TestHookDidSendFile(dstFD, uintptr(src), written, err, handled)
 	}()
 	if err := dstFD.writeLock(); err != nil {
 		return 0, err, false
diff --git a/src/internal/poll/sendfile_windows.go b/src/internal/poll/sendfile_windows.go
index f6d807d5d0..d72bcd5871 100644
--- a/src/internal/poll/sendfile_windows.go
+++ b/src/internal/poll/sendfile_windows.go
@@ -10,7 +10,7 @@ import (
 )
 
 // SendFile wraps the TransmitFile call.
-func SendFile(fd *FD, src syscall.Handle, size int64) (written int64, err error, handled bool) {
+func SendFile(fd *FD, src uintptr, size int64) (written int64, err error, handled bool) {
 	defer func() {
 		TestHookDidSendFile(fd, 0, written, err, written > 0)
 	}()
@@ -18,7 +18,8 @@ func SendFile(fd *FD, src syscall.Handle, size int64) (written int64, err error,
 		// TransmitFile does not work with pipes
 		return 0, syscall.ESPIPE, false
 	}
-	if ft, _ := syscall.GetFileType(src); ft == syscall.FILE_TYPE_PIPE {
+	hsrc := syscall.Handle(src)
+	if ft, _ := syscall.GetFileType(hsrc); ft == syscall.FILE_TYPE_PIPE {
 		return 0, syscall.ESPIPE, false
 	}
 
@@ -29,11 +30,11 @@ func SendFile(fd *FD, src syscall.Handle, size int64) (written int64, err error,
 
 	// Get the file size so we don't read past the end of the file.
 	var fi syscall.ByHandleFileInformation
-	if err := syscall.GetFileInformationByHandle(src, &fi); err != nil {
+	if err := syscall.GetFileInformationByHandle(hsrc, &fi); err != nil {
 		return 0, err, false
 	}
 	fileSize := int64(fi.FileSizeHigh)<<32 + int64(fi.FileSizeLow)
-	startpos, err := syscall.Seek(src, 0, io.SeekCurrent)
+	startpos, err := syscall.Seek(hsrc, 0, io.SeekCurrent)
 	if err != nil {
 		return 0, err, false
 	}
@@ -49,7 +50,7 @@ func SendFile(fd *FD, src syscall.Handle, size int64) (written int64, err error,
 			// Some versions of Windows (Windows 10 1803) do not set
 			// file position after TransmitFile completes.
 			// So just use Seek to set file position.
-			_, serr := syscall.Seek(src, startpos+written, io.SeekStart)
+			_, serr := syscall.Seek(hsrc, startpos+written, io.SeekStart)
 			if err != nil {
 				err = serr
 			}
@@ -62,7 +63,7 @@ func SendFile(fd *FD, src syscall.Handle, size int64) (written int64, err error,
 	const maxChunkSizePerCall = int64(0x7fffffff - 1)
 
 	o := &fd.wop
-	o.handle = src
+	o.handle = hsrc
 	for size > 0 {
 		chunkSize := maxChunkSizePerCall
 		if chunkSize > size {
diff --git a/src/net/sendfile_unix_alt.go b/src/net/sendfile.go
similarity index 89%
rename from src/net/sendfile_unix_alt.go
rename to src/net/sendfile.go
index db788753f1..0a41241561 100644
--- a/src/net/sendfile_unix_alt.go
+++ b/src/net/sendfile.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (darwin && !ios) || dragonfly || freebsd || solaris
+//go:build linux || (darwin && !ios) || dragonfly || freebsd || solaris || windows
 
 package net
 
@@ -44,7 +44,7 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 
 	var werr error
 	err = sc.Read(func(fd uintptr) bool {
-		written, werr, handled = poll.SendFile(&c.pfd, int(fd), remain)
+		written, werr, handled = poll.SendFile(&c.pfd, fd, remain)
 		return true
 	})
 	if err == nil {
diff --git a/src/net/sendfile_linux.go b/src/net/sendfile_linux.go
deleted file mode 100644
index 75af617416..0000000000
--- a/src/net/sendfile_linux.go
+++ /dev/null
@@ -1,55 +0,0 @@
-// Copyright 2011 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package net
-
-import (
-	"internal/poll"
-	"io"
-	"os"
-)
-
-const supportsSendfile = true
-
-// sendFile copies the contents of r to c using the sendfile
-// system call to minimize copies.
-//
-// if handled == true, sendFile returns the number (potentially zero) of bytes
-// copied and any non-EOF error.
-//
-// if handled == false, sendFile performed no work.
-func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
-	var remain int64 = 0 // 0 indicates sending until EOF
-
-	lr, ok := r.(*io.LimitedReader)
-	if ok {
-		remain, r = lr.N, lr.R
-		if remain <= 0 {
-			return 0, nil, true
-		}
-	}
-	f, ok := r.(*os.File)
-	if !ok {
-		return 0, nil, false
-	}
-
-	sc, err := f.SyscallConn()
-	if err != nil {
-		return 0, nil, false
-	}
-
-	var werr error
-	err = sc.Read(func(fd uintptr) bool {
-		written, werr, handled = poll.SendFile(&c.pfd, int(fd), remain)
-		return true
-	})
-	if err == nil {
-		err = werr
-	}
-
-	if lr != nil {
-		lr.N = remain - written
-	}
-	return written, wrapSyscallError("sendfile", err), handled
-}
diff --git a/src/net/sendfile_test.go b/src/net/sendfile_test.go
index 2b23f86ff0..b5039ff1d1 100644
--- a/src/net/sendfile_test.go
+++ b/src/net/sendfile_test.go
@@ -49,7 +49,7 @@ func expectSendfile(t *testing.T, wantConn Conn, f func()) {
 		gotFD      *poll.FD
 		gotErr     error
 	)
-	poll.TestHookDidSendFile = func(dstFD *poll.FD, src int, written int64, err error, handled bool) {
+	poll.TestHookDidSendFile = func(dstFD *poll.FD, src uintptr, written int64, err error, handled bool) {
 		if called {
 			t.Error("internal/poll.SendFile called multiple times, want one call")
 		}
diff --git a/src/net/sendfile_windows.go b/src/net/sendfile_windows.go
deleted file mode 100644
index 731528f716..0000000000
--- a/src/net/sendfile_windows.go
+++ /dev/null
@@ -1,61 +0,0 @@
-// Copyright 2011 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package net
-
-import (
-	"internal/poll"
-	"io"
-	"syscall"
-)
-
-const supportsSendfile = true
-
-// TODO: deduplicate this file with sendfile_linux.go and sendfile_unix_alt.go.
-
-// sendFile copies the contents of r to c using the sendfile
-// system call to minimize copies.
-//
-// if handled == true, sendFile returns the number (potentially zero) of bytes
-// copied and any non-EOF error.
-//
-// if handled == false, sendFile performed no work.
-func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
-	var remain int64 = 0 // by default, copy until EOF.
-
-	lr, ok := r.(*io.LimitedReader)
-	if ok {
-		remain, r = lr.N, lr.R
-		if remain <= 0 {
-			return 0, nil, true
-		}
-	}
-
-	// r might be an *os.File or an os.fileWithoutWriteTo.
-	// Type assert to an interface rather than *os.File directly to handle the latter case.
-	f, ok := r.(syscall.Conn)
-	if !ok {
-		return 0, nil, false
-	}
-
-	sc, err := f.SyscallConn()
-	if err != nil {
-		return 0, nil, false
-	}
-
-	var werr error
-	err = sc.Read(func(fd uintptr) bool {
-		written, werr, handled = poll.SendFile(&c.pfd, syscall.Handle(fd), remain)
-		return true
-	})
-	if err == nil {
-		err = werr
-	}
-
-	if lr != nil {
-		lr.N = remain - written
-	}
-
-	return written, wrapSyscallError("sendfile", err), handled
-}
diff --git a/src/os/readfrom_solaris_test.go b/src/os/readfrom_solaris_test.go
index b11fbef0ff..b460f4c113 100644
--- a/src/os/readfrom_solaris_test.go
+++ b/src/os/readfrom_solaris_test.go
@@ -48,10 +48,10 @@ func hookSendFileTB(tb testing.TB) *copyFileHook {
 	tb.Cleanup(func() {
 		poll.TestHookDidSendFile = orig
 	})
-	poll.TestHookDidSendFile = func(dstFD *poll.FD, src int, written int64, err error, handled bool) {
+	poll.TestHookDidSendFile = func(dstFD *poll.FD, src uintptr, written int64, err error, handled bool) {
 		hook.called = true
 		hook.dstfd = dstFD.Sysfd
-		hook.srcfd = src
+		hook.srcfd = int(src)
 		hook.written = written
 		hook.err = err
 		hook.handled = handled
diff --git a/src/os/writeto_linux_test.go b/src/os/writeto_linux_test.go
index 59caecd0da..7d11bda74f 100644
--- a/src/os/writeto_linux_test.go
+++ b/src/os/writeto_linux_test.go
@@ -111,10 +111,10 @@ func hookSendFile(t *testing.T) *sendFileHook {
 	t.Cleanup(func() {
 		poll.TestHookDidSendFile = orig
 	})
-	poll.TestHookDidSendFile = func(dstFD *poll.FD, src int, written int64, err error, handled bool) {
+	poll.TestHookDidSendFile = func(dstFD *poll.FD, src uintptr, written int64, err error, handled bool) {
 		h.called = true
 		h.dstfd = dstFD.Sysfd
-		h.srcfd = src
+		h.srcfd = int(src)
 		h.written = written
 		h.err = err
 		h.handled = handled
diff --git a/src/os/zero_copy_linux.go b/src/os/zero_copy_linux.go
index 9d666a3c79..af30a68168 100644
--- a/src/os/zero_copy_linux.go
+++ b/src/os/zero_copy_linux.go
@@ -28,7 +28,7 @@ func (f *File) writeTo(w io.Writer) (written int64, handled bool, err error) {
 	}
 
 	rerr := sc.Read(func(fd uintptr) (done bool) {
-		written, err, handled = poll.SendFile(pfd, int(fd), 0)
+		written, err, handled = poll.SendFile(pfd, fd, 0)
 		return true
 	})
 
diff --git a/src/os/zero_copy_solaris.go b/src/os/zero_copy_solaris.go
index 94a8de6062..6000700fce 100644
--- a/src/os/zero_copy_solaris.go
+++ b/src/os/zero_copy_solaris.go
@@ -78,7 +78,7 @@ func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
 	// https://docs.oracle.com/cd/E88353_01/html/E37843/sendfile-3c.html and
 	// https://illumos.org/man/3EXT/sendfile for more details.
 	rerr := sc.Read(func(fd uintptr) bool {
-		written, err, handled = poll.SendFile(&f.pfd, int(fd), remain)
+		written, err, handled = poll.SendFile(&f.pfd, fd, remain)
 		return true
 	})
 	if lr != nil {