diff --git a/crates/ui-egui/src/canvas/tool_input.rs b/crates/ui-egui/src/canvas/tool_input.rs
index 7d4b17e166..ed69d3d909 100644
--- a/crates/ui-egui/src/canvas/tool_input.rs
+++ b/crates/ui-egui/src/canvas/tool_input.rs
@@ -525,7 +525,12 @@ pub(super) fn tool_event_with_view(app: &mut PhotocraftApp, ev: ToolEvent, mods:
             if !sets_source && press_refused(app, tool) {
                 return;
             }
-            if !sets_source && (crate::rasterize_prompt::intercept(app, tool, x, y, pressure) || refuse_group(app, tool)) {
+            // The Clone Stamp's no-source alert opens at the press, after any rasterize prompt.
+            if !sets_source
+                && (crate::rasterize_prompt::intercept(app, tool, x, y, pressure)
+                    || refuse_group(app, tool)
+                    || crate::retouch_ui::clone_stamp_without_source(app, tool))
+            {
                 return;
             }
             // ⌘ with a selection tool is the Move tool for the drag: outside the selection (or
diff --git a/crates/ui-egui/src/tools/retouch_ui.rs b/crates/ui-egui/src/tools/retouch_ui.rs
index 58aac368db..7576c7dee3 100644
--- a/crates/ui-egui/src/tools/retouch_ui.rs
+++ b/crates/ui-egui/src/tools/retouch_ui.rs
@@ -198,6 +198,21 @@ pub(crate) fn stroke_seed(points: &[[f64; 3]]) -> u64 {
     photocraft_engine::paint::rng::seed_from_bytes(first.as_bytes())
 }
 
+/// A Clone Stamp press with no source point yet: the reference application's alert, opened at
+/// the press (#12609) and once while it is up. Returns whether it refused the stroke.
+pub(crate) fn clone_stamp_without_source(app: &mut PhotocraftApp, tool: Tool) -> bool {
+    if tool != Tool::CloneStamp || clone_params(app).is_some() {
+        return false;
+    }
+    let message = if cfg!(target_os = "macos") {
+        tl!("Could not use the clone stamp tool because the area to clone has not been defined (Option-click to define a source point).")
+    } else {
+        tl!("Could not use the clone stamp tool because the area to clone has not been defined (Alt-click to define a source point).")
+    };
+    open_alert_once(app, message);
+    true
+}
+
 /// Finish a stroke with a retouching tool. Returns false if `tool` isn't one.
 pub fn finish_stroke(app: &mut PhotocraftApp, tool: Tool, points: &[[f64; 3]], mods: egui::Modifiers, line: bool) -> bool {
     finish_stroke_with(app, tool, points, mods, line, None)
@@ -224,6 +239,9 @@ pub(crate) fn finish_stroke_with(app: &mut PhotocraftApp, tool: Tool, points: &[
                 return true;
             }
             let Some(p) = clone_params(app) else {
+                if clone_stamp_without_source(app, tool) {
+                    return true;
+                }
                 // Option-click on the Mac, Alt-click on Windows.
                 app.ui.status = if cfg!(target_os = "macos") {
                     tl!("Option-click to define a source point to clone from")
@@ -783,7 +801,8 @@ fn cam_amount_slider(ui: &mut egui::Ui, name: &str, value: &mut f32, lo: f32, hi
     });
 }
 
-fn open_cam_range_alert(app: &mut PhotocraftApp, message: &str) {
+/// Opens the alert with `message` (English, translated here) unless it is already up.
+fn open_alert_once(app: &mut PhotocraftApp, message: &str) {
     let message = tl!(message).to_owned();
     let shown =
         app.ui.dialogs.iter().any(|d| d.kind == crate::state::DialogKind::Error && d.fields.get("message").and_then(|m| m.as_str()) == Some(message.as_str()));
@@ -807,11 +826,11 @@ fn content_aware_move_bar(app: &mut PhotocraftApp, ui: &mut egui::Ui) {
         }
         opt(ui, tl!("Structure:"));
         if cam_integer_popup(ui, "cam-structure", "Structure", &mut app.ui.tool_options.cam_structure, 1.0, 7.0, STRUCTURE_TIP) {
-            open_cam_range_alert(app, STRUCTURE_RANGE_ALERT);
+            open_alert_once(app, STRUCTURE_RANGE_ALERT);
         }
         opt(ui, tl!("Color:"));
         if cam_integer_popup(ui, "cam-color", "Color", &mut app.ui.tool_options.cam_color, 0.0, 10.0, COLOR_TIP) {
-            open_cam_range_alert(app, COLOR_RANGE_ALERT);
+            open_alert_once(app, COLOR_RANGE_ALERT);
         }
         crate::widgets::checkbox(ui, &mut app.ui.tool_options.sample_all.content_aware_move, tl!("Sample All Layers"))
             .on_hover_text(tl!("Enable to remix all layers"));
diff --git a/crates/ui-egui/src/tools/retouch_ui/tests.rs b/crates/ui-egui/src/tools/retouch_ui/tests.rs
index a6eba29bd2..545e475ae4 100644
--- a/crates/ui-egui/src/tools/retouch_ui/tests.rs
+++ b/crates/ui-egui/src/tools/retouch_ui/tests.rs
@@ -225,15 +225,15 @@ fn paint_bucket_mode_reaches_the_fill() {
 
 #[test]
 fn clone_without_a_source_names_the_platform_modifier() {
-    // Option-click on the Mac, Alt-click elsewhere (#251).
-    for tool in [Tool::CloneStamp, Tool::Healing] {
-        let mut app = app();
-        app.ui.tool = tool;
-        assert!(finish_stroke(&mut app, tool, &[[10.0, 30.0, 1.0], [50.0, 30.0, 1.0]], egui::Modifiers::NONE, false));
-        assert!(app.ui.status_error, "{tool:?}");
-        let want = if cfg!(target_os = "macos") { "Option-click" } else { "Alt-click" };
-        assert!(app.ui.status.starts_with(want), "{tool:?}: {}", app.ui.status);
-    }
+    // Option-click on the Mac, Alt-click elsewhere (#251). The Clone Stamp says it in an alert
+    // (#12609, clone_stamp_no_source_alert_tests.rs).
+    let tool = Tool::Healing;
+    let mut app = app();
+    app.ui.tool = tool;
+    assert!(finish_stroke(&mut app, tool, &[[10.0, 30.0, 1.0], [50.0, 30.0, 1.0]], egui::Modifiers::NONE, false));
+    assert!(app.ui.status_error);
+    let want = if cfg!(target_os = "macos") { "Option-click" } else { "Alt-click" };
+    assert!(app.ui.status.starts_with(want), "{}", app.ui.status);
 }
 
 #[test]