diff --git a/crates/fj-core/src/operations/split/half_edge.rs b/crates/fj-core/src/operations/split/half_edge.rs
index 24a88f186..9279599a8 100644
--- a/crates/fj-core/src/operations/split/half_edge.rs
+++ b/crates/fj-core/src/operations/split/half_edge.rs
@@ -52,7 +52,10 @@ impl SplitHalfEdge for Handle<HalfEdge> {
         .insert(core)
         .derive_from(self, core)
         .set_geometry(
-            core.layers.geometry.of_half_edge(self),
+            core.layers
+                .geometry
+                .of_half_edge(self)
+                .with_boundary([start, point]),
             &mut core.layers.geometry,
         );
         let b = HalfEdge::new(
@@ -63,7 +66,10 @@ impl SplitHalfEdge for Handle<HalfEdge> {
         .insert(core)
         .derive_from(self, core)
         .set_geometry(
-            core.layers.geometry.of_half_edge(self),
+            core.layers
+                .geometry
+                .of_half_edge(self)
+                .with_boundary([point, end]),
             &mut core.layers.geometry,
         );