1 files changed, 11 insertions, 2 deletions
diff --git a/src/net/sendfile_unix_alt.go b/src/net/sendfile_unix_alt.go
index 5cb65ee767..9e46c4e607 100644
--- a/src/net/sendfile_unix_alt.go
+++ b/src/net/sendfile_unix_alt.go
@@ -9,9 +9,12 @@ package net
 import (
 	"internal/poll"
 	"io"
-	"os"
+	"io/fs"
+	"syscall"
 )
 
+const supportsSendfile = true
+
 // sendFile copies the contents of r to c using the sendfile
 // system call to minimize copies.
 //
@@ -34,7 +37,13 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 			return 0, nil, true
 		}
 	}
-	f, ok := r.(*os.File)
+	// 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.(interface {
+		fs.File
+		io.Seeker
+		syscall.Conn
+	})
 	if !ok {
 		return 0, nil, false
 	}