diff --git a/crates/ailang-core/src/workspace.rs b/crates/ailang-core/src/workspace.rs
index 650cf1f..eb3caab 100644
--- a/crates/ailang-core/src/workspace.rs
+++ b/crates/ailang-core/src/workspace.rs
@@ -575,15 +575,22 @@ fn build_registry(
     // step at the same type-hash.
     for (key, entry) in entries.iter() {
         let (class_name, type_hash) = key;
+        let type_repr = type_head_name(&entry.instance.type_);
+        // Iter 22b.2 leaves superclass-cycle detection to a future arm;
+        // here we just terminate the walk.
+        let mut visited: BTreeSet<&str> = BTreeSet::new();
         let mut current = class_by_name.get(class_name.as_str()).copied();
         while let Some(c) = current {
+            if !visited.insert(c.name.as_str()) {
+                break;
+            }
             if let Some(sc) = &c.superclass {
                 let sc_key = (sc.class.clone(), type_hash.clone());
                 if !entries.contains_key(&sc_key) {
                     return Err(WorkspaceLoadError::MissingSuperclassInstance {
                         class: class_name.clone(),
                         superclass: sc.class.clone(),
-                        type_repr: type_head_name(&entry.instance.type_),
+                        type_repr: type_repr.clone(),
                     });
                 }
                 current = class_by_name.get(sc.class.as_str()).copied();