diff --git a/crates/engine/src/cmd/path.rs b/crates/engine/src/cmd/path.rs
index fb63bf12e..f1bc3e501 100644
--- a/crates/engine/src/cmd/path.rs
+++ b/crates/engine/src/cmd/path.rs
@@ -112,7 +112,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Convert Anchor Points",
             [],
             None,
-            "{to: \"corner\"|\"smooth\"} convert the direct-selected anchors (all anchors of fully selected paths, every point of a selected blend's spine) as one undo step: corner retracts both handles, smooth pulls handles in line with the neighbours (smooth anchors keep theirs)",
+            "{to: \"corner\"|\"smooth\"} convert the direct-selected anchors (all anchors of fully selected paths, every point of a selected blend's spine; a spine from Replace Spine changes only its handles, its points and the keys' spread along it staying as they are) as one undo step: corner retracts both handles, smooth pulls handles in line with the neighbours (smooth anchors keep theirs)",
             has_selection,
             convert_anchors
         ),
@@ -1155,11 +1155,7 @@ fn convert_anchors(s: &mut Session, p: &Value) -> Result<Value> {
                 }
             }
         }
-        for id in &blends {
-            let Some(NodeKind::Blend { children, spec }) = d.node_mut(*id).map(|n| &mut n.kind) else { continue };
-            let Some((mut path, anchors)) = vectorcraft_doc::live::pin_spine(children, spec) else { continue };
-            let pinned = path.clone();
-            let Some(sp) = path.subpaths.first_mut() else { continue };
+        let convert = |sp: &mut SubPath| {
             for ai in 0..sp.anchors.len() {
                 if smooth {
                     sp.smooth_anchor(ai);
@@ -1167,6 +1163,21 @@ fn convert_anchors(s: &mut Session, p: &Value) -> Result<Value> {
                     a.retract();
                 }
             }
+        };
+        for id in &blends {
+            let Some(NodeKind::Blend { children, spec }) = d.node_mut(*id).map(|n| &mut n.kind) else { continue };
+            // A spine from Replace Spine keeps its points and its keys spread along it: only the
+            // handles change, and the keys are not pinned to points.
+            if vectorcraft_doc::live::blend_spine(children, spec).is_some_and(|(_, anchors)| anchors.is_none()) {
+                if let Some(sp) = spec.spine.as_mut().and_then(|p| p.subpaths.first_mut()) {
+                    convert(sp);
+                }
+                continue;
+            }
+            let Some((mut path, anchors)) = vectorcraft_doc::live::pin_spine(children, spec) else { continue };
+            let pinned = path.clone();
+            let Some(sp) = path.subpaths.first_mut() else { continue };
+            convert(sp);
             // A spine the conversion leaves as it was stays as the blend has it.
             if path != pinned {
                 spec.key_anchors = anchors.iter().map(|a| u32::try_from(*a).unwrap_or(u32::MAX)).collect();
diff --git a/crates/engine/src/tests/blendspine.rs b/crates/engine/src/tests/blendspine.rs
index 0ab2aac5b..5db598a19 100644
--- a/crates/engine/src/tests/blendspine.rs
+++ b/crates/engine/src/tests/blendspine.rs
@@ -144,6 +144,42 @@ fn converting_anchors_of_a_selected_blend_converts_its_spine() {
     assert_eq!(spec(&s, g).spine.unwrap().subpaths[0].anchors[1], middle, "one undo step");
 }
 
+/// Converting the points of a blend whose spine came from Replace Spine changes only the spine's
+/// handles: its points stay where they are, the keys are not pinned to points, and the steps stay
+/// spread along the spine instead of the spine's ends moving onto the keys.
+#[test]
+fn converting_anchors_of_a_replaced_spine_changes_only_its_handles() {
+    let mut s = session();
+    let (_, _, g) = blend(&mut s);
+    let spine = id_of(&s.execute("path.create", &json!({"d": "M100 300 L200 200 L300 300"})).unwrap());
+    s.execute("select.set", &json!({"ids": [g.0, spine.0]})).unwrap();
+    s.execute("object.blend.replaceSpine", &json!({})).unwrap();
+    s.execute("select.set", &json!({"ids": [g.0]})).unwrap();
+    let points = |s: &Session| spec(s, g).spine.unwrap().subpaths[0].anchors.iter().map(|a| a.p).collect::<Vec<_>>();
+    let before = points(&s);
+    let ends = |s: &Session| {
+        let st = steps(s, g);
+        (center(&st[0]), center(&st[st.len() - 1]))
+    };
+    let ends_before = ends(&s);
+    s.execute("path.convertAnchors", &json!({"to": "smooth"})).unwrap();
+    let sp = spec(&s, g);
+    assert!(sp.key_anchors.is_empty(), "{:?}", sp.key_anchors);
+    assert_eq!(points(&s), before, "the spine's points stay put");
+    let middle = sp.spine.as_ref().unwrap().subpaths[0].anchors[1];
+    assert!(middle.has_in() && middle.has_out(), "{middle:?}");
+    assert_eq!(ends(&s), ends_before, "the end steps stay at the spine's ends");
+    assert!(center(&steps(&s, g)[1]).distance(Point::new(200.0, 200.0)) < 1e-6, "the step stays on the spine");
+
+    s.execute("path.convertAnchors", &json!({"to": "corner"})).unwrap();
+    let sp = spec(&s, g);
+    assert!(sp.key_anchors.is_empty(), "{:?}", sp.key_anchors);
+    assert!(sp.spine.unwrap().subpaths[0].anchors.iter().all(|a| !a.has_in() && !a.has_out()));
+    assert_eq!(points(&s), before);
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert_eq!(spec(&s, g).spine.unwrap().subpaths[0].anchors[1], middle, "one undo step");
+}
+
 #[test]
 fn moving_a_key_point_moves_the_key_and_the_other_way_round() {
     let mut s = session();