diff --git a/codex-rs/tui/src/app/event_dispatch.rs b/codex-rs/tui/src/app/event_dispatch.rs
index 2e2b910a4a..b30db31905 100644
--- a/codex-rs/tui/src/app/event_dispatch.rs
+++ b/codex-rs/tui/src/app/event_dispatch.rs
@@ -2525,8 +2525,10 @@ impl App {
                     }
                     Err(err) => {
                         tracing::error!(error = %err, "failed to persist service tier selection");
+                        let error = format_config_error(&err);
                         self.chat_widget.add_error_message(format!(
-                            "Failed to save default service tier: {err}"
+                            "Failed to save default service tier: {error}\n\
+                             You can continue this task. To save the default, resolve the error above, then switch to a different tier and back to the desired tier."
                         ));
                     }
                 }
diff --git a/codex-rs/tui/src/app/tests/model_defaults_tests.rs b/codex-rs/tui/src/app/tests/model_defaults_tests.rs
index 882196edeb..12a0785507 100644
--- a/codex-rs/tui/src/app/tests/model_defaults_tests.rs
+++ b/codex-rs/tui/src/app/tests/model_defaults_tests.rs
@@ -164,9 +164,18 @@ async fn model_default_saves_report_server_outcomes_and_target_server_profile()
         ] {
             Box::pin(app.handle_event(&mut tui, &mut server, event)).await?;
         }
+        let mut service_tier_error = None;
         let messages = std::iter::from_fn(|| events.try_recv().ok())
             .filter_map(|event| match event {
                 AppEvent::InsertHistoryCell(cell) => {
+                    if outcome == "rejected" {
+                        let text = lines_to_single_string(&cell.transcript_lines(/*width*/ 200));
+                        if text.contains("Failed to save default service tier") {
+                            service_tier_error = Some(
+                                text.replace(&profile_path.display().to_string(), "<config-path>"),
+                            );
+                        }
+                    }
                     Some(lines_to_single_string(&cell.transcript_lines(/*width*/ 80)))
                 }
                 _ => None,
@@ -186,6 +195,10 @@ async fn model_default_saves_report_server_outcomes_and_target_server_profile()
         }
         let persisted = std::fs::read_to_string(&profile_path)?;
         if outcome == "rejected" {
+            insta::assert_snapshot!(
+                "service_tier_default_save_error",
+                service_tier_error.expect("expected a service-tier save error")
+            );
             assert_eq!(persisted, "[broken");
             assert!(!messages.contains("Model changed"));
             assert!(!messages.contains("Service tier set"));
diff --git a/codex-rs/tui/src/app/tests/snapshots/codex_tui__app__tests__model_defaults__service_tier_default_save_error.snap b/codex-rs/tui/src/app/tests/snapshots/codex_tui__app__tests__model_defaults__service_tier_default_save_error.snap
new file mode 100644
index 0000000000..4e34b16db3
--- /dev/null
+++ b/codex-rs/tui/src/app/tests/snapshots/codex_tui__app__tests__model_defaults__service_tier_default_save_error.snap
@@ -0,0 +1,6 @@
+---
+source: tui/src/app/tests/model_defaults_tests.rs
+expression: "service_tier_error.expect(\"expected a service-tier save error\")"
+---
+■ Failed to save default service tier: config/batchWrite failed in TUI: config/batchWrite failed: failed to load configuration: <config-path>:1:8: unclosed table, expected `]` (code -32603)
+You can continue this task. To save the default, resolve the error above, then switch to a different tier and back to the desired tier.