diff --git a/compiler/sset.lisp b/compiler/sset.lisp
index a703973bcbca4855bdbdcebc48957c0c633f6d68..a79d3c8f2aa27cb13fde6bf7193160160ffa0b18 100644
--- a/compiler/sset.lisp
+++ b/compiler/sset.lisp
@@ -23,7 +23,7 @@
 ;;; operations.)
 ;;;
 (defstruct sset-element
-  (number nil :type (or unsigned-byte null)))
+  (number nil :type (or index null)))
 
 
 (defstruct (sset (:constructor make-sset ())