diff --git a/crates/ui-egui/src/formula_bar.rs b/crates/ui-egui/src/formula_bar.rs
index 753585f10..75d0020db 100644
--- a/crates/ui-egui/src/formula_bar.rs
+++ b/crates/ui-egui/src/formula_bar.rs
@@ -65,7 +65,7 @@ pub fn show(app: &mut SheetApp, ui: &mut egui::Ui) {
 fn active_input(app: &SheetApp) -> String {
     let Some(d) = app.session.active() else { return String::new() };
     let Some(sh) = d.wb.active() else { return String::new() };
-    let a = d.selection.active;
+    let a = sh.merge_at(d.selection.active).map(|m| m.start).unwrap_or(d.selection.active);
     if let Some(c) = sh.cell(a) {
         if c.formula.is_some() && d.wb.styles.get(c.style).protection.hidden && sh.is_protected() {
             return String::new();
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index 8eb1eca1a..d89165650 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -276,7 +276,7 @@ impl SheetApp {
     pub fn begin_edit(&mut self, text: Option<String>, from_formula_bar: bool) {
         let Some(d) = self.session.active() else { return };
         let Some(sh) = d.wb.active() else { return };
-        let at = d.selection.active;
+        let at = sh.merge_at(d.selection.active).map(|m| m.start).unwrap_or(d.selection.active);
         let current = sh.cell(at).map(|c| c.input_text()).unwrap_or_default();
         let (text, replace) = match text {
             Some(t) => (t, true),
diff --git a/crates/ui-egui/tests/merged_cells.rs b/crates/ui-egui/tests/merged_cells.rs
new file mode 100644
index 000000000..c28e0806e
--- /dev/null
+++ b/crates/ui-egui/tests/merged_cells.rs
@@ -0,0 +1,118 @@
+//! Merged-cell edits must read and write the visible, top-left cell.
+
+use egui::{Event, Key, Modifiers, PointerButton, Pos2};
+use egui_kittest::kittest::Queryable as _;
+use gridcraft_engine::Session;
+use gridcraft_engine::core::{CellRef, Value};
+use gridcraft_ui_egui::{SheetApp, grid::Geo};
+use serde_json::json;
+
+type Harness = egui_kittest::Harness<'static, SheetApp>;
+
+fn harness(input: &str) -> Harness {
+    let mut session = Session::new();
+    session.new_workbook();
+    session.execute("home.mergeCells", json!({"range": "A1:B2"})).unwrap();
+    session.execute("cell.set", json!({"cell": "A1", "input": input})).unwrap();
+    let mut h = egui_kittest::Harness::builder().with_size(egui::vec2(1200.0, 800.0)).build_ui_state(
+        |ui, app: &mut SheetApp| {
+            app.logic(ui.ctx());
+            app.ui(ui);
+        },
+        SheetApp::new(session, Default::default()),
+    );
+    h.run_steps(4);
+    h
+}
+
+fn cell_center(h: &Harness, cell: &str) -> Pos2 {
+    let app = h.state();
+    let sheet = app.session.active().unwrap().wb.active().unwrap();
+    let geo = Geo::new(sheet, app.grid.rect.unwrap(), app.view().scroll);
+    geo.cell_rect(sheet, CellRef::parse(cell).unwrap()).center()
+}
+
+fn click_cell(h: &mut Harness, cell: &str) {
+    let pos = cell_center(h, cell);
+    h.input_mut().events.extend([
+        Event::PointerMoved(pos),
+        Event::PointerButton { pos, button: PointerButton::Primary, pressed: true, modifiers: Modifiers::NONE },
+        Event::PointerButton { pos, button: PointerButton::Primary, pressed: false, modifiers: Modifiers::NONE },
+    ]);
+    h.run_steps(2);
+}
+
+fn text(h: &mut Harness, text: &str) {
+    h.input_mut().events.push(Event::Text(text.into()));
+    h.run_steps(2);
+}
+
+fn key(h: &mut Harness, key: Key) {
+    for pressed in [true, false] {
+        h.input_mut().events.push(Event::Key { key, physical_key: None, pressed, repeat: false, modifiers: Modifiers::NONE });
+    }
+    h.run_steps(2);
+}
+
+fn value(h: &Harness, cell: &str) -> Value {
+    h.state().session.active().unwrap().wb.active().unwrap().value(CellRef::parse(cell).unwrap())
+}
+
+#[test]
+fn typing_into_a_covered_cell_remains_visible_after_clicking_away() {
+    let mut h = harness("");
+    click_cell(&mut h, "B2");
+    assert_eq!(h.state().session.active().unwrap().selection.active.a1(), "B2");
+    text(&mut h, "hello");
+    click_cell(&mut h, "D4");
+
+    assert!(h.state().editor.is_none());
+    assert_eq!(value(&h, "A1"), Value::from("hello"), "the cell painted for the merge must contain the committed text");
+    assert_eq!(value(&h, "B2"), Value::Empty, "editing a merge must not hide text in a covered cell");
+    click_cell(&mut h, "B2");
+    assert!(h.query_by_label("hello").is_some(), "the formula bar must show the merged content when a covered cell is selected");
+}
+
+#[test]
+fn f2_and_double_click_edit_the_existing_merged_content() {
+    let mut h = harness("before");
+    click_cell(&mut h, "B2");
+    key(&mut h, Key::F2);
+    let editor = h.state().editor.as_ref().unwrap();
+    assert_eq!(editor.cell.a1(), "A1");
+    assert_eq!(editor.text, "before");
+    text(&mut h, "!");
+    key(&mut h, Key::Enter);
+    assert_eq!(value(&h, "A1"), Value::from("before!"));
+
+    click_cell(&mut h, "D4");
+    click_cell(&mut h, "B2");
+    click_cell(&mut h, "B2");
+    let editor = h.state().editor.as_ref().unwrap();
+    assert_eq!(editor.cell.a1(), "A1");
+    assert_eq!(editor.text, "before!");
+    text(&mut h, " again");
+    click_cell(&mut h, "D4");
+    assert_eq!(value(&h, "A1"), Value::from("before! again"));
+    assert_eq!(value(&h, "B2"), Value::Empty);
+}
+
+#[test]
+fn formula_bar_reads_and_edits_the_merge_anchor_from_a_covered_cell() {
+    let mut h = harness("formula bar text");
+    click_cell(&mut h, "B2");
+    h.get_by_label("formula bar text").click();
+    h.run_steps(2);
+
+    let editor = h.state().editor.as_ref().unwrap();
+    assert!(editor.from_formula_bar);
+    assert_eq!(editor.cell.a1(), "A1");
+    assert_eq!(editor.text, "formula bar text");
+    text(&mut h, " edited");
+    key(&mut h, Key::Enter);
+    assert_eq!(value(&h, "A1"), Value::from("formula bar text edited"));
+    assert_eq!(value(&h, "B2"), Value::Empty);
+    click_cell(&mut h, "D4");
+    click_cell(&mut h, "B2");
+    assert!(h.query_by_label("formula bar text edited").is_some());
+}