Corrected tracing.

diff --git a/npvm.lisp b/npvm.lisp
index d645bba..8e92762 100644
--- a/npvm.lisp
+++ b/npvm.lisp
@@ -183,7 +183,7 @@
       (vm-dump vm))
     (handler-case
         (loop
-          (when trace (vm-disassemble program pc))
+          (when trace (vm-disassemble vm pc))
           (macrolet ((next-instruction ()
                        `(aref program (prog1 pc (incf pc)))))
             (let ((code (next-instruction)))