diff --git a/compiler/vmdef.lisp b/compiler/vmdef.lisp
index 86c63fe2855d28e3f6db02eecb7e0964dece3c71..6554da2e009f9bf37f0b3ecb5f8bc97641467391 100644
--- a/compiler/vmdef.lisp
+++ b/compiler/vmdef.lisp
@@ -227,6 +227,13 @@
        (setf (sc-sb (sc-or-lose ',name)) (sb-or-lose ',sb-name))
        ',name)))
 
+
+;;;; Side-Effect Classes
+
+(def-boolean-attribute vop
+  any)
+
+
 
 ;;;; Move/coerce definition: