diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 1e37f5636506ae1f2eccaabf698c7bdfefe5eec6..d6d44aa775289a9dbee95f7edaac8c5e2181d30a 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -56,6 +56,7 @@ stderr_writer: File.Writer = .{
     .io = undefined,
     .interface = Io.File.Writer.initInterface(&.{}),
     .file = if (is_windows) undefined else .stderr(),
+    .mode = .streaming,
 },
 stderr_mode: Io.Terminal.Mode = .no_color,
 stderr_writer_initialized: bool = false,