diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 13b49b1c09..a402ef3f58 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -816,6 +816,12 @@ impl Session {
                             }
                             Err(error) => {
                                 warn!("failed to prepare undo patch: {error:#}");
+                                self.clear_last_undo_patch();
+                                self.notify_background_event(
+                                    &context.sub_id,
+                                    format!("Undo is unavailable for this turn: {error:#}"),
+                                )
+                                .await;
                             }
                         }
                     }
@@ -827,6 +833,17 @@ impl Session {
                 }
                 Err(error) => {
                     warn!("failed to compute unified diff: {error:#}");
+                    if *exit_code == 0 {
+                        self.clear_last_undo_patch();
+                        self
+                            .notify_background_event(
+                                &context.sub_id,
+                                format!(
+                                    "Undo is unavailable for this turn: failed to compute diff: {error:#}"
+                                ),
+                            )
+                            .await;
+                    }
                 }
             }
         }
diff --git a/codex-rs/tui/src/chatwidget.rs b/codex-rs/tui/src/chatwidget.rs
index 4ad80a03d0..60678b7427 100644
--- a/codex-rs/tui/src/chatwidget.rs
+++ b/codex-rs/tui/src/chatwidget.rs
@@ -1267,21 +1267,21 @@ impl ChatWidget {
             tx.send(AppEvent::CodexOp(Op::UndoLastTurnDiff));
         })];
 
-        let mut items = Vec::new();
-        items.push(SelectionItem {
+        let items = vec![
+        SelectionItem {
             name: "Undo last turn diff".to_string(),
             description: Some(
                 "Revert files that Codex changed during the most recent turn.".to_string(),
             ),
             is_current: false,
             actions: undo_actions,
-        });
-        items.push(SelectionItem {
+        },
+        SelectionItem {
             name: "Cancel".to_string(),
             description: Some("Close without undoing any files.".to_string()),
             is_current: false,
             actions: Vec::new(),
-        });
+        }];
 
         self.bottom_pane.show_selection_view(
             "Undo last Codex turn?".to_string(),