diff --git a/crates/fj-core/src/validate/shell.rs b/crates/fj-core/src/validate/shell.rs
index 20a4c966a..e54800f30 100644
--- a/crates/fj-core/src/validate/shell.rs
+++ b/crates/fj-core/src/validate/shell.rs
@@ -9,7 +9,10 @@ use crate::{
     },
     storage::Handle,
     topology::{Curve, HalfEdge, Shell, Vertex},
-    validation::{checks::CurveGeometryMismatch, ValidationCheck},
+    validation::{
+        checks::{CurveGeometryMismatch, HalfEdgeHasNoSibling},
+        ValidationCheck,
+    },
 };
 
 use super::{Validate, ValidationConfig, ValidationError};
@@ -36,11 +39,8 @@ impl Validate for Shell {
 #[derive(Clone, Debug, thiserror::Error)]
 pub enum ShellValidationError {
     /// [`Shell`] contains a half-edge that is not part of a pair
-    #[error("Half-edge has no sibling: {half_edge:#?}")]
-    HalfEdgeHasNoSibling {
-        /// The half-edge that has no sibling
-        half_edge: Handle<HalfEdge>,
-    },
+    #[error("Half-edge has no sibling: {:#?}", .0.half_edge)]
+    HalfEdgeHasNoSibling(HalfEdgeHasNoSibling),
 
     /// [`Shell`] contains half-edges that are coincident, but aren't siblings
     #[error(
@@ -114,7 +114,10 @@ impl ShellValidationError {
         }
 
         for half_edge in unmatched_half_edges.into_values().cloned() {
-            errors.push(Self::HalfEdgeHasNoSibling { half_edge }.into());
+            errors.push(
+                Self::HalfEdgeHasNoSibling(HalfEdgeHasNoSibling { half_edge })
+                    .into(),
+            );
         }
     }
 
diff --git a/crates/fj-core/src/validation/checks/half_edge_siblings.rs b/crates/fj-core/src/validation/checks/half_edge_siblings.rs
new file mode 100644
index 000000000..71e06b226
--- /dev/null
+++ b/crates/fj-core/src/validation/checks/half_edge_siblings.rs
@@ -0,0 +1,18 @@
+use crate::{storage::Handle, topology::HalfEdge};
+
+/// A [`Shell`] contains a [`HalfEdge`] without a sibling
+///
+/// Half-edges that are coincident must reference the same curve. This makes
+/// those half-edges siblings.
+///
+/// In a shell, every half-edge must have a sibling. If that is not the case,
+/// this is a sign of either of the following:
+/// - That the shell is not closed, meaning it has some kind of hole.
+/// - If the shell is closed, that its topological object graph is not valid.
+///
+/// [`Shell`]: crate::topology::Shell
+#[derive(Clone, Debug)]
+pub struct HalfEdgeHasNoSibling {
+    /// The half-edge that does not have a sibling
+    pub half_edge: Handle<HalfEdge>,
+}
diff --git a/crates/fj-core/src/validation/checks/mod.rs b/crates/fj-core/src/validation/checks/mod.rs
index ec0b68aa5..c66e63357 100644
--- a/crates/fj-core/src/validation/checks/mod.rs
+++ b/crates/fj-core/src/validation/checks/mod.rs
@@ -6,10 +6,12 @@ mod curve_geometry_mismatch;
 mod face_boundary;
 mod face_winding;
 mod half_edge_connection;
+mod half_edge_siblings;
 
 pub use self::{
     curve_geometry_mismatch::CurveGeometryMismatch,
     face_boundary::FaceHasNoBoundary,
     face_winding::InteriorCycleHasInvalidWinding,
     half_edge_connection::AdjacentHalfEdgesNotConnected,
+    half_edge_siblings::HalfEdgeHasNoSibling,
 };