diff --git a/scp.c b/scp.c
index a3e2b4f4..392f2728 100644
--- a/scp.c
+++ b/scp.c
@@ -5812,7 +5812,7 @@ if (!(uptr->flags & UNIT_ATT)) {                        /* not attached? */
     }
 if ((dptr = find_dev_from_unit (uptr)) == NULL)
     return SCPE_OK;
-if (uptr->flags & UNIT_BUF) {
+if ((uptr->flags & UNIT_BUF) && (uptr->filebuf)) {
     uint32 cap = (uptr->hwmark + dptr->aincr - 1) / dptr->aincr;
     if (uptr->hwmark && ((uptr->flags & UNIT_RO) == 0)) {
         if (!sim_quiet) {