diff --git a/crates/erg_compiler/context/unify.rs b/crates/erg_compiler/context/unify.rs
index 39db7936f..9e3e68829 100644
--- a/crates/erg_compiler/context/unify.rs
+++ b/crates/erg_compiler/context/unify.rs
@@ -193,10 +193,10 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
                             // self.occur_inner(&sup_t, maybe_sup)
                         })?;
                     }
-                    if let Some((_sub_t, sup_t)) = sup.get_subsup() {
+                    if let Some((sub_t, sup_t)) = sup.get_subsup() {
                         sup.do_avoiding_recursion(|| {
                             // occur(?U, ?T(:> ?U or Y)) ==> OK
-                            // self.occur_inner(maybe_sub, &sub_t)?;
+                            self.occur_inner(maybe_sub, &sub_t)?;
                             self.occur_inner(maybe_sub, &sup_t)
                         })?;
                     }
diff --git a/crates/erg_compiler/tests/infer.er b/crates/erg_compiler/tests/infer.er
index e4b4b749a..a4bcf1406 100644
--- a/crates/erg_compiler/tests/infer.er
+++ b/crates/erg_compiler/tests/infer.er
@@ -48,3 +48,10 @@ ff! x: Str or NoneType =
         do!: f0!()
 f0!() = print! ""
 f1! _: Str = f0!()
+
+arr = [1]
+for! arr, (_,) =>
+    if! True, do!:
+        if! True, do!:
+            if! True, do!:
+                todo()