diff --git a/compiler/old-rt/vm.lisp b/compiler/old-rt/vm.lisp
index ee4434839691825e69a93ad2b2befba508faa74e..9108a902e59abad00fef248321ce3e59de42b982 100644
--- a/compiler/old-rt/vm.lisp
+++ b/compiler/old-rt/vm.lisp
@@ -124,6 +124,9 @@
 ;;; be primitive types.
 (def-primitive-type list (descriptor-reg))
 
+;;; Dummy primitive type for catch block TNs.
+(def-primitive-type catch-block (stack) :type nil)
+
 
 ;;; Primitive-Type-Of  --  Interface
 ;;;