diff --git a/lib/std/Io/Dispatch.zig b/lib/std/Io/Dispatch.zig
index 8c1ba1c80559390bb39eb06dd1dccb054b80b9bf..851ed34156737103639d12f03170e74bd2500e79 100644
--- a/lib/std/Io/Dispatch.zig
+++ b/lib/std/Io/Dispatch.zig
@@ -4908,7 +4908,7 @@ fn netWriteFileUnavailable(
     _ = header;
     _ = file_reader;
     _ = limit;
-    return error.NetworkDown;
+    return error.Unimplemented;
 }
 
 fn netClose(userdata: ?*anyopaque, handles: []const net.Socket.Handle) void {
diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index d4b202e12d0fa9087716209c24215bc179d71c1a..52b530c8eb11acb08083589ba865e0fa733b226c 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -11378,7 +11378,8 @@ fn netWriteFile(
     _ = header;
     _ = file_reader;
     _ = limit;
-    @panic("TODO implement netWriteFile");
+    // TODO implement netWriteFile
+    return error.Unimplemented;
 }
 
 fn fileWriteFilePositional(
diff --git a/lib/std/Io/Uring.zig b/lib/std/Io/Uring.zig
index e560500a755281510f64954d12040b1b6c5504b4..436406174b5643ef3c50df54e8e65b12ba5bd597 100644
--- a/lib/std/Io/Uring.zig
+++ b/lib/std/Io/Uring.zig
@@ -5183,7 +5183,7 @@ fn netWriteFileUnavailable(
     _ = header;
     _ = file_reader;
     _ = limit;
-    return error.NetworkDown;
+    return error.Unimplemented;
 }
 
 fn netClose(userdata: ?*anyopaque, handles: []const net.Socket.Handle) void {
diff --git a/lib/std/Io/net.zig b/lib/std/Io/net.zig
index 6611502cc157238167445e516cb5ea5b6a0af832..a546552cb9c7bb24ced83e88fbae4946f21a7061 100644
--- a/lib/std/Io/net.zig
+++ b/lib/std/Io/net.zig
@@ -1350,9 +1350,17 @@ pub const Stream = struct {
             SocketNotBound,
         } || Io.UnexpectedError || Io.Cancelable;
 
-        pub const WriteFileError = error{
-            NetworkDown,
-        } || Io.Cancelable || Io.UnexpectedError;
+        pub const WriteFileError = Error || error{
+            /// The `Io` implementation cannot offer a more efficient
+            /// file-to-socket path; the caller should fall back to read-based
+            /// copying. See `Io.Writer.sendFile`.
+            Unimplemented,
+            /// Reached the end of the file being read.
+            EndOfStream,
+            /// The source `File.Reader` failed; detailed diagnostics are found
+            /// on that struct.
+            ReadFailed,
+        };
 
         pub fn init(stream: Stream, io: Io, buffer: []u8) Writer {
             return .{
@@ -1381,10 +1389,25 @@ pub const Stream = struct {
         }
 
         fn sendFile(io_w: *Io.Writer, file_reader: *Io.File.Reader, limit: Io.Limit) Io.Writer.FileError!usize {
-            _ = io_w;
-            _ = file_reader;
-            _ = limit;
-            return error.Unimplemented; // TODO
+            const w: *Writer = @alignCast(@fieldParentPtr("interface", io_w));
+            const io = w.io;
+            const header = io_w.buffered();
+            const handle = w.stream.socket.handle;
+            const n = io.vtable.netWriteFile(io.userdata, handle, header, file_reader, limit) catch |err| switch (err) {
+                error.Canceled => {
+                    w.err = error.Canceled;
+                    return error.WriteFailed;
+                },
+                error.EndOfStream,
+                error.Unimplemented,
+                error.ReadFailed,
+                => |e| return e,
+                else => |e| {
+                    w.write_file_err = e;
+                    return error.WriteFailed;
+                },
+            };
+            return io_w.consume(n);
         }
     };