diff --git a/src/ir/lower.zig b/src/ir/lower.zig
index 2fb0ad8..22620bd 100644
--- a/src/ir/lower.zig
+++ b/src/ir/lower.zig
@@ -1992,6 +1992,16 @@ pub const Lowering = struct {
                                         break :blk self.emitPlaceholder(eff_fn_name);
                                     }
                                 }
+                                // NOTE: `xx <sx_fn> : *void` (e.g.
+                                // `class_addMethod(_, _, xx my_imp, _)`)
+                                // is intentionally NOT diagnosed here.
+                                // Manually-constructed Closure values
+                                // legitimately store default-conv sx fns
+                                // into a `*void` slot for sx-side dispatch
+                                // through the closure trampoline ABI. The
+                                // compiler can't distinguish C-side vs
+                                // sx-side use from the cast alone.
+                                // examples/50-smoke.sx has both shapes.
                             }
                         }
                         break :blk self.builder.emit(.{ .func_ref = fid }, .s64);