diff --git a/src/termio/Thread.zig b/src/termio/Thread.zig
index f24fcf0df..d61301f5c 100644
--- a/src/termio/Thread.zig
+++ b/src/termio/Thread.zig
@@ -202,7 +202,7 @@ fn threadMain_(self: *Thread, io: *termio.Termio) !void {
 
     // Get the writer. This must be a mailbox writer for threading.
     const writer = switch (io.writer) {
-        .mailbox => |v| v,
+        .mailbox => |*v| v,
         // else => return error.TermioUnsupportedWriter,
     };