diff --git a/crates/engine/src/edit/run.rs b/crates/engine/src/edit/run.rs
index 8734c372b7..703d1b2cc0 100644
--- a/crates/engine/src/edit/run.rs
+++ b/crates/engine/src/edit/run.rs
@@ -296,6 +296,16 @@ pub(crate) fn run_edit(doc: &mut pdfcraft_cos::Document, edit: &Edit, cx: &mut E
             if levels.is_empty() {
                 return Err(EditError::Invalid("choose a text style for at least one bookmark level".into()));
             }
+            // Each line goes to the first level whose style it is in: a style given again, or one
+            // within the size tolerance of an earlier level's, would leave its level empty.
+            for (i, a) in levels.iter().enumerate() {
+                if let Some(j) = levels.iter().skip(i.saturating_add(1)).position(|b| a.matches(b)) {
+                    let (first, second) = (i.saturating_add(1), i.saturating_add(j).saturating_add(2));
+                    return Err(EditError::Invalid(format!(
+                        "bookmark levels {first} and {second} have the same text style: choose a different one for each level"
+                    )));
+                }
+            }
             let entries = crate::text_style_bookmarks::headings(doc, levels);
             if entries.is_empty() {
                 return Err(EditError::Invalid("no text is set in the chosen styles".into()));
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 5dbcb7d81b..6439ba6363 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -1927,6 +1927,24 @@ fn bookmarks_from_text_styles_nest_the_headings_and_undo() {
     assert!(s.get(id).unwrap().info.outline.is_empty());
 }
 
+/// CodeRabbit on #4560: a line goes to the first level whose style it is in, so the same style
+/// for two levels (or one within the size tolerance of the other) would leave the later level
+/// empty. Refused at the edit, for the dialog and automation alike; nothing changes.
+#[test]
+fn bookmarks_from_text_styles_refuse_one_style_for_two_levels() {
+    let mut s = Session::new();
+    let id = s.open("styled.pdf", None, Arc::new(styled_headings_fixture()), None).unwrap();
+    let styles = s.get(id).unwrap().text_styles();
+    let (chapter, section) = (styles[0].style.clone(), styles[1].style.clone());
+    let near = pdfcraft_engine_style(&section, section.size + 0.1);
+    for levels in [vec![chapter.clone(), chapter.clone()], vec![chapter.clone(), section.clone(), near]] {
+        let n = levels.len();
+        let err = s.apply(id, Edit::BookmarksFromTextStyles { levels }).unwrap_err();
+        assert!(err.to_string().contains(&format!("levels {} and {n} have the same text style", n - 1)), "{err}");
+        assert!(s.get(id).unwrap().info.outline.is_empty());
+    }
+}
+
 /// CodeRabbit on #4560: bookmark titles from text styles are the document's text, so a document
 /// that forbids copying lists no styles and refuses the edit, as it refuses other extraction.
 #[test]
@@ -8849,69 +8867,69 @@ fn pdf_with_annots(annots: &[&[u8]]) -> Vec<u8> {
     bytes
 }
 
-/// ISO 32000-2 Table 224 (`/NeedAppearances`) and Table 192 (`/MK /CA`): a form that leaves its
-/// appearances to the viewer shows its check boxes and radio buttons drawn from `/MK`, over the
-/// filled squares the file carries: a checked box its check mark (ZapfDingbats `4`), an unchecked
-/// one its empty border, a radio button its dot (`l`), on screen and printed as an image. Without
-/// `/NeedAppearances` the file's own squares show. Saving writes the file as it was.
-#[test]
-fn need_appearances_buttons_are_displayed_from_their_captions() {
-    let pdf = |need: bool| {
-        let flag = if need { "/NeedAppearances true " } else { "" };
-        format!(
-            "%PDF-1.7\n\
-             1 0 obj << /Type /Catalog /Pages 2 0 R /AcroForm 4 0 R >> endobj\n\
-             2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 >> endobj\n\
-             3 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 400 200] /Annots [6 0 R 7 0 R 8 0 R] >> endobj\n\
-             4 0 obj << /Fields [6 0 R 7 0 R 8 0 R] {flag}/DA (/Helv 0 Tf 0 g) /DR << /Font << /Helv 5 0 R >> >> >> endobj\n\
-             5 0 obj << /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >> endobj\n\
-             6 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /T (on) /V /Yes /AS /Yes /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (4) >> /Rect [20 100 60 140] /F 4 /P 3 0 R /AP << /N << /Yes 9 0 R /Off 9 0 R >> >> >> endobj\n\
-             7 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /T (off) /V /Off /AS /Off /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (4) >> /Rect [100 100 140 140] /F 4 /P 3 0 R /AP << /N << /Yes 9 0 R /Off 9 0 R >> >> >> endobj\n\
-             8 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /Ff 32768 /T (radio) /V /B /AS /B /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (l) >> /Rect [180 100 220 140] /F 4 /P 3 0 R /AP << /N << /B 9 0 R /Off 9 0 R >> >> >> endobj\n\
-             9 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 40 40] /Length 18 >> stream\n0 g 4 4 32 32 re f\nendstream endobj\n\
-             trailer << /Root 1 0 R >>\n%%EOF"
-        )
-        .into_bytes()
-    };
-    let render = |bytes: Arc<Vec<u8>>| {
-        let mut r = pdfcraft_render::PageRenderer::new(bytes, pdfcraft_render::RenderConfig::default());
-        r.render(pdfcraft_render::RenderRequest { page: 0, scale: 1.0, ..Default::default() })
-    };
-    // Dark pixels of the page (drawn at scale 1, 400 x 200) in the user-space box x0..x1, y0..y1.
-    let ink = |page: &pdfcraft_render::RenderedPage, (x0, y0, x1, y1): (u32, u32, u32, u32)| {
-        let (px, _) = page.rgba.as_chunks::<4>();
-        (200 - y1..200 - y0)
-            .flat_map(|y| (x0..x1).map(move |x| (x, y)))
-            .filter(|&(x, y)| px.get((y * page.width + x) as usize).is_some_and(|p| p[0] < 128 && p[1] < 128 && p[2] < 128))
-            .count()
-    };
-    // In a widget whose lower-left corner is (x, y): its whole inside, the top-left of its inside
-    // (where a check mark leaves the box empty), and the lower-left corner (outside a dot).
-    let inside = |x: u32, y: u32| (x + 6, y + 6, x + 34, y + 34);
-    let top_left = |x: u32, y: u32| (x + 6, y + 26, x + 14, y + 34);
-    let corner = |x: u32, y: u32| (x + 5, y + 5, x + 9, y + 9);
-    let mut s = Session::new();
-    let id = s.open("form.pdf", None, Arc::new(pdf(true)), None).unwrap();
-    let shown = render(s.get(id).unwrap().display.clone());
-    let raster = pdfcraft_print::Raster { dpi: 72.0, grayscale: false };
-    let pictures = crate::print_raster::rasterize(s.get(id).unwrap(), &[0], &raster, pdfcraft_print::Content::Document).unwrap();
-    let printed = render(Arc::new(pictures));
-    for (page, how) in [(&shown, "shown"), (&printed, "printed")] {
-        let (check, check_corner) = (ink(page, inside(20, 100)), ink(page, top_left(20, 100)));
-        assert!(check > 100 && check < 600, "{how}: a check mark, not the 28 x 28 square: {check}");
-        assert_eq!(check_corner, 0, "{how}: the check mark leaves the top left empty");
-        assert_eq!(ink(page, inside(100, 100)), 0, "{how}: the unchecked box is empty");
-        assert!(ink(page, (100, 100, 140, 102)) > 30, "{how}: and keeps its border");
-        let dot = ink(page, (188, 108, 212, 132));
-        assert!(dot > 300 && ink(page, corner(180, 100)) == 0, "{how}: the radio button's dot: {dot}");
-    }
-    let saved = s.save_bytes(id).unwrap();
-    assert!(saved.windows(18).any(|w| w == b"0 g 4 4 32 32 re f"), "the file keeps its own appearances");
-
-    // Without /NeedAppearances the file's filled squares are shown.
-    let id = s.open("plain.pdf", None, Arc::new(pdf(false)), None).unwrap();
-    let shown = render(s.get(id).unwrap().display.clone());
-    for x in [20, 100, 180] {
-        assert!(ink(&shown, inside(x, 100)) > 700, "the file's square at {x}");
-    }
-}
+/// ISO 32000-2 Table 224 (`/NeedAppearances`) and Table 192 (`/MK /CA`): a form that leaves its
+/// appearances to the viewer shows its check boxes and radio buttons drawn from `/MK`, over the
+/// filled squares the file carries: a checked box its check mark (ZapfDingbats `4`), an unchecked
+/// one its empty border, a radio button its dot (`l`), on screen and printed as an image. Without
+/// `/NeedAppearances` the file's own squares show. Saving writes the file as it was.
+#[test]
+fn need_appearances_buttons_are_displayed_from_their_captions() {
+    let pdf = |need: bool| {
+        let flag = if need { "/NeedAppearances true " } else { "" };
+        format!(
+            "%PDF-1.7\n\
+             1 0 obj << /Type /Catalog /Pages 2 0 R /AcroForm 4 0 R >> endobj\n\
+             2 0 obj << /Type /Pages /Kids [3 0 R] /Count 1 >> endobj\n\
+             3 0 obj << /Type /Page /Parent 2 0 R /MediaBox [0 0 400 200] /Annots [6 0 R 7 0 R 8 0 R] >> endobj\n\
+             4 0 obj << /Fields [6 0 R 7 0 R 8 0 R] {flag}/DA (/Helv 0 Tf 0 g) /DR << /Font << /Helv 5 0 R >> >> >> endobj\n\
+             5 0 obj << /Type /Font /Subtype /Type1 /BaseFont /Helvetica /Encoding /WinAnsiEncoding >> endobj\n\
+             6 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /T (on) /V /Yes /AS /Yes /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (4) >> /Rect [20 100 60 140] /F 4 /P 3 0 R /AP << /N << /Yes 9 0 R /Off 9 0 R >> >> >> endobj\n\
+             7 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /T (off) /V /Off /AS /Off /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (4) >> /Rect [100 100 140 140] /F 4 /P 3 0 R /AP << /N << /Yes 9 0 R /Off 9 0 R >> >> >> endobj\n\
+             8 0 obj << /Type /Annot /Subtype /Widget /FT /Btn /Ff 32768 /T (radio) /V /B /AS /B /DA (/Helv 0 Tf 0 g) /MK << /BC [0 0 0] /CA (l) >> /Rect [180 100 220 140] /F 4 /P 3 0 R /AP << /N << /B 9 0 R /Off 9 0 R >> >> >> endobj\n\
+             9 0 obj << /Type /XObject /Subtype /Form /BBox [0 0 40 40] /Length 18 >> stream\n0 g 4 4 32 32 re f\nendstream endobj\n\
+             trailer << /Root 1 0 R >>\n%%EOF"
+        )
+        .into_bytes()
+    };
+    let render = |bytes: Arc<Vec<u8>>| {
+        let mut r = pdfcraft_render::PageRenderer::new(bytes, pdfcraft_render::RenderConfig::default());
+        r.render(pdfcraft_render::RenderRequest { page: 0, scale: 1.0, ..Default::default() })
+    };
+    // Dark pixels of the page (drawn at scale 1, 400 x 200) in the user-space box x0..x1, y0..y1.
+    let ink = |page: &pdfcraft_render::RenderedPage, (x0, y0, x1, y1): (u32, u32, u32, u32)| {
+        let (px, _) = page.rgba.as_chunks::<4>();
+        (200 - y1..200 - y0)
+            .flat_map(|y| (x0..x1).map(move |x| (x, y)))
+            .filter(|&(x, y)| px.get((y * page.width + x) as usize).is_some_and(|p| p[0] < 128 && p[1] < 128 && p[2] < 128))
+            .count()
+    };
+    // In a widget whose lower-left corner is (x, y): its whole inside, the top-left of its inside
+    // (where a check mark leaves the box empty), and the lower-left corner (outside a dot).
+    let inside = |x: u32, y: u32| (x + 6, y + 6, x + 34, y + 34);
+    let top_left = |x: u32, y: u32| (x + 6, y + 26, x + 14, y + 34);
+    let corner = |x: u32, y: u32| (x + 5, y + 5, x + 9, y + 9);
+    let mut s = Session::new();
+    let id = s.open("form.pdf", None, Arc::new(pdf(true)), None).unwrap();
+    let shown = render(s.get(id).unwrap().display.clone());
+    let raster = pdfcraft_print::Raster { dpi: 72.0, grayscale: false };
+    let pictures = crate::print_raster::rasterize(s.get(id).unwrap(), &[0], &raster, pdfcraft_print::Content::Document).unwrap();
+    let printed = render(Arc::new(pictures));
+    for (page, how) in [(&shown, "shown"), (&printed, "printed")] {
+        let (check, check_corner) = (ink(page, inside(20, 100)), ink(page, top_left(20, 100)));
+        assert!(check > 100 && check < 600, "{how}: a check mark, not the 28 x 28 square: {check}");
+        assert_eq!(check_corner, 0, "{how}: the check mark leaves the top left empty");
+        assert_eq!(ink(page, inside(100, 100)), 0, "{how}: the unchecked box is empty");
+        assert!(ink(page, (100, 100, 140, 102)) > 30, "{how}: and keeps its border");
+        let dot = ink(page, (188, 108, 212, 132));
+        assert!(dot > 300 && ink(page, corner(180, 100)) == 0, "{how}: the radio button's dot: {dot}");
+    }
+    let saved = s.save_bytes(id).unwrap();
+    assert!(saved.windows(18).any(|w| w == b"0 g 4 4 32 32 re f"), "the file keeps its own appearances");
+
+    // Without /NeedAppearances the file's filled squares are shown.
+    let id = s.open("plain.pdf", None, Arc::new(pdf(false)), None).unwrap();
+    let shown = render(s.get(id).unwrap().display.clone());
+    for x in [20, 100, 180] {
+        assert!(ink(&shown, inside(x, 100)) > 700, "the file's square at {x}");
+    }
+}
diff --git a/crates/engine/src/text_style_bookmarks.rs b/crates/engine/src/text_style_bookmarks.rs
index 07a0cacd78..5969188d67 100644
--- a/crates/engine/src/text_style_bookmarks.rs
+++ b/crates/engine/src/text_style_bookmarks.rs
@@ -24,7 +24,7 @@ pub struct TextStyle {
 impl TextStyle {
     /// Whether `other` is this style. Sizes within a quarter point match, as the same heading
     /// size is often written with rounding differences (12 and 11.96).
-    fn matches(&self, other: &TextStyle) -> bool {
+    pub(crate) fn matches(&self, other: &TextStyle) -> bool {
         self.font == other.font && self.bold == other.bold && self.italic == other.italic && (self.size - other.size).abs() <= SIZE_TOLERANCE
     }
 }