diff --git a/src/main.rs b/src/main.rs
index 0254c67..98ea6cb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -75,5 +75,14 @@ async fn main() -> Result<()> {
 fn init_tracing(verbose: bool) {
     let default = if verbose { "pixelpass=trace,iroh=info" } else { "pixelpass=info,iroh=warn" };
     let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(default));
-    tracing_subscriber::fmt().with_env_filter(filter).with_target(false).init();
+    // Tracing MUST write to stderr. `tracing_subscriber::fmt()` defaults its
+    // writer to stdout, but with `--output json` stdout carries the JSON event
+    // stream the `--gui` front-end parses (see `common::output`) — logging there
+    // interleaves log lines into that stream (corrupting events and starving the
+    // GUI's stderr-tail diagnostics). Pin it to stderr to honor that contract.
+    tracing_subscriber::fmt()
+        .with_writer(std::io::stderr)
+        .with_env_filter(filter)
+        .with_target(false)
+        .init();
 }