diff --git a/crates/idml/src/export.rs b/crates/idml/src/export.rs
index 717bb5d6c..0c85e8f8a 100644
--- a/crates/idml/src/export.rs
+++ b/crates/idml/src/export.rs
@@ -106,6 +106,8 @@ struct Ex<'a> {
     /// Index topic path → first serialized sort key; See / See also cross-references.
     index_topics: BTreeMap<Vec<String>, String>,
     index_xrefs: Vec<(Vec<String>, &'static str, String)>,
+    /// Object style name → whether its chain or `[None]` sets corners, found once per style.
+    style_corners: HashMap<String, bool>,
 }
 
 impl<'a> Ex<'a> {
@@ -121,6 +123,7 @@ impl<'a> Ex<'a> {
             link_text_sources: Vec::new(),
             index_topics: BTreeMap::new(),
             index_xrefs: Vec::new(),
+            style_corners: HashMap::new(),
         };
         ex.assign_swatch_ids();
         for s in d.stories.values() {
diff --git a/crates/idml/src/export/item.rs b/crates/idml/src/export/item.rs
index 469053c2f..3c240deca 100644
--- a/crates/idml/src/export/item.rs
+++ b/crates/idml/src/export/item.rs
@@ -87,8 +87,10 @@ impl<'a> Ex<'a> {
             el.set("GradientStrokeAngle", num(a));
         }
         self.stroke_attrs(&mut el, &it.stroke);
-        // Corner options: map path-order corners to the named corners by geometry.
-        if !it.corners.is_none() {
+        // Corner options: map path-order corners to the named corners by geometry. An item without
+        // corners whose object style chain sets some writes None, so an import does not give it
+        // the style's corners.
+        if !it.corners.is_none() || self.style_sets_corners(os) {
             let names_by_index = corner_names(&it.path);
             for (i, c) in it.corners.corners.iter().enumerate() {
                 let n = names_by_index[i];
@@ -153,6 +155,36 @@ impl<'a> Ex<'a> {
         el
     }
 
+    /// Whether object style `name`, a style it is based on, or `[None]` (which an import reads
+    /// after every item's style chain) sets corners other than None. A built-in style the
+    /// document lacks counts as its default.
+    fn style_sets_corners(&mut self, name: &str) -> bool {
+        if let Some(&known) = self.style_corners.get(name) {
+            return known;
+        }
+        let defaults = designcraft_doc::Styles::default();
+        let style = |n: &str| self.d.styles.object_style(n).or_else(|| defaults.object_style(n));
+        let rounds = |os: &designcraft_doc::ObjectStyle| os.corners.is_some_and(|c| !c.is_none());
+        let mut seen: Vec<&str> = Vec::new();
+        let mut cur = Some(name);
+        let mut found = false;
+        while let Some(n) = cur.take() {
+            if seen.contains(&n) {
+                break;
+            }
+            let Some(os) = style(n) else { break };
+            if rounds(os) {
+                found = true;
+                break;
+            }
+            seen.push(n);
+            cur = os.based_on.as_deref();
+        }
+        let found = found || style(designcraft_doc::NO_OBJECT_STYLE).is_some_and(rounds);
+        self.style_corners.insert(name.to_string(), found);
+        found
+    }
+
     fn append_transparency(&self, el: &mut El, it: &Item, os: &str) {
         // Transparency.
         // An item whose style sets effects writes the effects it has turned off too, so that on
diff --git a/crates/idml/src/tests/object_styles.rs b/crates/idml/src/tests/object_styles.rs
index 4ff0fa6bf..6226d4a74 100644
--- a/crates/idml/src/tests/object_styles.rs
+++ b/crates/idml/src/tests/object_styles.rs
@@ -232,6 +232,43 @@ fn exported_frames_keep_their_own_values_over_their_object_style() {
     assert_eq!(got.options, want);
 }
 
+/// Items without corners keep none after export and import, though their object style, the style
+/// it is based on, or `[None]` (read after every style chain) sets rounded corners.
+#[test]
+fn exported_frames_keep_no_corners_over_their_object_style() {
+    let mut d = small_doc();
+    let lid = d.default_layer();
+    let id = designcraft_doc::ItemId(d.alloc());
+    let rect = designcraft_doc::Item::new(id, lid, Shape::Rectangle, shapes::rectangle(Rect::new(40.0, 420.0, 200.0, 500.0)));
+    d.insert_item(SpreadRef::Doc(0), rect, None).unwrap();
+    let rounded = Some(designcraft_geom::corners::CornerOptions {
+        corners: [designcraft_geom::corners::Corner { shape: CornerShape::Rounded, size: 12.0 }; 4],
+    });
+    let styles = std::sync::Arc::make_mut(&mut d.styles);
+    styles.object.push(designcraft_doc::ObjectStyle { name: "Round".into(), corners: rounded, ..Default::default() });
+    styles.object.push(designcraft_doc::ObjectStyle { name: "Child".into(), based_on: Some("Round".into()), ..Default::default() });
+    match styles.object.iter_mut().find(|o| o.name == designcraft_doc::NO_OBJECT_STYLE) {
+        Some(none) => none.corners = rounded,
+        None => {
+            styles.object.push(designcraft_doc::ObjectStyle { name: designcraft_doc::NO_OBJECT_STYLE.into(), corners: rounded, ..Default::default() })
+        }
+    }
+    styles.object.push(designcraft_doc::ObjectStyle { name: "Plain".into(), ..Default::default() });
+    let names = ["Round", "Child", designcraft_doc::NO_OBJECT_STYLE, "Plain"];
+    let ids: Vec<_> = d.spreads.iter().flat_map(|s| s.items.iter().map(|i| i.id)).take(4).collect();
+    assert_eq!(ids.len(), 4);
+    for (id, style) in ids.iter().zip(names) {
+        let it = d.item_mut(*id).unwrap();
+        it.object_style = style.into();
+        assert!(it.corners.is_none());
+    }
+    let back = import_idml(&export_idml(&d)).unwrap();
+    for style in names {
+        let it = back.spreads.iter().flat_map(|s| s.items.iter()).find(|i| i.object_style == style).unwrap();
+        assert!(it.corners.is_none(), "{style}: {:?}", it.corners);
+    }
+}
+
 #[test]
 fn text_wrap_side_and_contour_come_from_the_style_for_frames_and_placed_graphics() {
     let styles = r#"<ObjectStyle Self="ObjectStyle/Contour" Name="Contour">