diff --git a/crates/engine/src/cmd/insert.rs b/crates/engine/src/cmd/insert.rs
index 3c45031af..9719bf451 100644
--- a/crates/engine/src/cmd/insert.rs
+++ b/crates/engine/src/cmd/insert.rs
@@ -1317,9 +1317,20 @@ fn comment(s: &mut Session, p: &Json, threaded: bool) -> Result<Json> {
     let sheet = target_sheet(s, p)?;
     let at = cell_param_on(s, p, "cell", sheet)?.unwrap_or(s.doc()?.selection.active);
     let text = str_param(p, "text").unwrap_or("").to_string();
-    let author = str_param(p, "author").map(str::to_string).unwrap_or_else(|| s.prefs.user_name.clone());
+    let named = str_param(p, "author").map(str::to_string);
+    let author = named.clone().unwrap_or_else(|| s.prefs.user_name.clone());
     edit(s, |cx| {
-        cx.sheet_mut(sheet)?.comments.insert(
+        let comments = &mut cx.sheet_mut(sheet)?.comments;
+        // Writing a note on a cell that has one edits it, as Excel's Edit Note does: the box, the
+        // replies, the dates and who wrote it stay. A note replaces a comment and vice versa.
+        if let Some(c) = comments.get_mut(&at).filter(|c| c.threaded == threaded) {
+            c.text = text.clone();
+            if let Some(author) = named.clone() {
+                c.author = author;
+            }
+            return Ok(json!({"cell": at.a1()}));
+        }
+        comments.insert(
             at,
             Comment {
                 author: author.clone(),
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index ecadd0766..46cc1f5f4 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -3851,6 +3851,35 @@ fn notes_comments_and_links_survive_a_json_save() {
     assert_eq!(after.cells, before.cells);
 }
 
+/// Writing a note or a comment on a cell that has one of the same kind edits its text: the
+/// replies, the resolved state, the dates and the note's box stay. `comment` replaced the whole
+/// thread, so editing a comment dropped its replies.
+#[test]
+fn editing_a_note_or_a_comment_keeps_its_thread() {
+    let mut s = s();
+    s.execute("review.newComment", json!({"cell": "B2", "text": "first", "author": "Ada"})).unwrap();
+    s.execute("review.replyComment", json!({"cell": "B2", "text": "reply", "author": "Bob"})).unwrap();
+    s.execute("review.resolveComment", json!({"cell": "B2", "resolved": true})).unwrap();
+    s.execute("review.newComment", json!({"cell": "B2", "text": "edited"})).unwrap();
+    s.execute("review.newNote", json!({"cell": "A1", "text": "note", "author": "Ada"})).unwrap();
+    s.execute("review.showNote", json!({"cell": "A1"})).unwrap();
+    s.execute("review.newNote", json!({"cell": "A1", "text": "changed"})).unwrap();
+    let d = s.doc().unwrap();
+    let sh = d.wb.active().unwrap();
+    let thread = &sh.comments[&CellRef::parse("B2").unwrap()];
+    assert_eq!((thread.author.as_str(), thread.text.as_str()), ("Ada", "edited"));
+    assert_eq!(thread.replies, vec![("Bob".to_string(), "reply".to_string())]);
+    assert!(thread.resolved && thread.threaded);
+    let note = &sh.comments[&CellRef::parse("A1").unwrap()];
+    assert_eq!((note.author.as_str(), note.text.as_str()), ("Ada", "changed"));
+    assert!(note.visible && !note.threaded);
+    // A note written over a comment replaces it.
+    s.execute("review.newNote", json!({"cell": "B2", "text": "plain"})).unwrap();
+    let d = s.doc().unwrap();
+    let replaced = &d.wb.active().unwrap().comments[&CellRef::parse("B2").unwrap()];
+    assert!(!replaced.threaded && replaced.replies.is_empty());
+}
+
 /// A cut moves the block's notes, hyperlinks and merged areas with it. The source's cells and
 /// pictures were removed but the block's merges and notes were not, so one merged block became
 /// two (an empty one left at the old place) and a note ended up on both the old and the new