diff --git a/crates/ui-egui/src/hotbar.rs b/crates/ui-egui/src/hotbar.rs
index a6bf36ec9f..328f85e706 100644
--- a/crates/ui-egui/src/hotbar.rs
+++ b/crates/ui-egui/src/hotbar.rs
@@ -343,8 +343,15 @@ fn active_tool_controls(ui: &mut egui::Ui, app: &mut PdfCraftApp, t: &Tokens, ve
                 (size.changed() && !size.dragged()) || size.drag_stopped()
             })
             .is_some_and(|popup| popup.inner);
-        if resized && let Some((page, index)) = selected_fill_text(app) {
-            app.apply_edit(Edit::FontSizeAnnotation { page, index, size: app.fill_text_size });
+        let size = app.fill_text_size;
+        if resized
+            && let Some((page, index)) = selected_fill_text(app)
+            && app
+                .active_ids()
+                .and_then(|(_, id)| app.session.get(id)?.comment_props(page, index)?.font_size)
+                .is_none_or(|stored| format!("{stored:.3}") != format!("{size:.3}"))
+        {
+            app.apply_edit(Edit::FontSizeAnnotation { page, index, size });
         }
     }
     if let QuickTool::Comment(tool) = app.quick_tool {
diff --git a/crates/ui-egui/tests/it/fill_sign.rs b/crates/ui-egui/tests/it/fill_sign.rs
index 979ba0ff97..931018214a 100644
--- a/crates/ui-egui/tests/it/fill_sign.rs
+++ b/crates/ui-egui/tests/it/fill_sign.rs
@@ -1896,6 +1896,62 @@ fn dragging_the_fill_text_size_slider_is_one_undo_step() {
     assert_eq!(placed_height(&h, "Drag me"), height, "one undo takes the whole drag back");
 }
 
+#[test]
+fn pressing_the_fill_text_size_slider_without_moving_it_adds_no_undo_step() {
+    let mut h = harness();
+    place_selected_text(&mut h, "Hold me");
+    let height = placed_height(&h, "Hold me");
+    h.get_by_label("Font size").click();
+    h.run_steps(2);
+    let slider = h.get_by_role(egui::accesskit::Role::Slider).rect();
+    let at = pos2(slider.min.x + (slider.max.x - slider.min.x) * 0.75, (slider.min.y + slider.max.y) / 2.0);
+    let press = |h: &mut Harness<'static, PdfCraftApp>| {
+        h.hover_at(at);
+        h.run_steps(1);
+        h.drag_at(at);
+        h.run_steps(1);
+        h.drop_at(at);
+        h.run_steps(3);
+    };
+    press(&mut h);
+    let resized = placed_height(&h, "Hold me");
+    assert!(resized > height, "the first press moves the size: {height} -> {resized}");
+    press(&mut h);
+    assert_eq!(placed_height(&h, "Hold me"), resized);
+    h.state_mut().execute("edit.undo");
+    h.run_steps(3);
+    assert_eq!(placed_height(&h, "Hold me"), height, "one undo takes back the only change; the second press added no step");
+}
+
+#[test]
+fn typing_a_fill_text_size_that_rounds_to_the_stored_one_adds_no_undo_step() {
+    let mut h = harness();
+    place_selected_text(&mut h, "Round me");
+    let height = placed_height(&h, "Round me");
+    h.get_by_label("Font size").click();
+    h.run_steps(2);
+    let type_size = |h: &mut Harness<'static, PdfCraftApp>, value: &str| {
+        h.query_all_by_role(egui::accesskit::Role::SpinButton)
+            .find(|n| n.value().is_some_and(|v| v.ends_with(" pt")))
+            .expect("the Font size control")
+            .click();
+        h.run_steps(2);
+        h.key_press_modifiers(egui::Modifiers::COMMAND, egui::Key::A);
+        h.event(egui::Event::Text(value.into()));
+        h.run_steps(1);
+        h.key_press(egui::Key::Enter);
+        h.run_steps(4);
+    };
+    type_size(&mut h, "36.1234");
+    let resized = placed_height(&h, "Round me");
+    assert!(resized > height, "the first size applies: {height} -> {resized}");
+    type_size(&mut h, "36.1231");
+    assert_eq!(h.state().fill_text_size, 36.1231);
+    h.state_mut().execute("edit.undo");
+    h.run_steps(3);
+    assert_eq!(placed_height(&h, "Round me"), height, "one undo takes back the only change; the rounded retype added no step");
+}
+
 #[test]
 fn the_fill_colour_dot_recolours_the_selected_text() {
     let mut h = harness();