diff --git a/os.rkt b/os.rkt
index 268ff83..67e5813 100644
--- a/os.rkt
+++ b/os.rkt
@@ -144,8 +144,8 @@
 ;; TODO: enforce user-mode restrictions
 ;; TODO: timeouts
 
-;; PatternPredicate BootK -> VM
-(define (make-vm pattern-predicate boot)
+;; BootK -> VM
+(define (make-vm boot #:pattern-predicate [pattern-predicate default-pattern-predicate])
   (vm (list)
       (make-queue)
       (make-queue)
@@ -289,7 +289,7 @@
 ;;   MetaMessage, MetaMessagePattern = not defined because there's no outer level
 ;; Runs its argument VM until it becomes (provably) inert.
 (define (ground-vm boot #:pattern-predicate [pattern-predicate default-pattern-predicate])
-  (let loop ((transition (run-vm (make-vm pattern-predicate boot))))
+  (let loop ((transition (run-vm (make-vm boot #:pattern-predicate pattern-predicate))))
     (for-each (lambda (thunk) (thunk)) (kernel-mode-transition-messages transition))
     (when (not (nested-vm-inert? (kernel-mode-transition-subscription transition)))
       (match transition