diff --git a/insns.def b/insns.def
index 2bdb2d5d7a..f912b51c87 100644
--- a/insns.def
+++ b/insns.def
@@ -210,6 +210,8 @@ getinstancevariable
 (ID id, IVC ic)
 ()
 (VALUE val)
+/* Ractor crashes when it accesses class/module-level instances variables. */
+// attr bool leaf = false; /* has IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR() */
 {
     val = vm_getinstancevariable(GET_ISEQ(), GET_SELF(), id, ic);
 }