diff --git a/compiler/vop.lisp b/compiler/vop.lisp
index 7e356001fd5f5b822ee114b2ef524bd8ff4decc4..830456bae7c200f31d1ffffebd626fb5c850eefa 100644
--- a/compiler/vop.lisp
+++ b/compiler/vop.lisp
@@ -948,7 +948,11 @@
 		 :type sc-vector)
   ;;
   ;; True if this SC or one of its alternates in in the NUMBER-STACK SB.
-  (number-stack-p nil :type boolean))
+  (number-stack-p nil :type boolean)
+
+  ;;
+  ;; Alignment restriction.  The offset must be an even multiple of this.
+  (alignment 1 :type (integer 1)))
 
 (defprinter sc
   name)