diff --git a/PDP11/pdp11_ng.c b/PDP11/pdp11_ng.c
index a2a9a2dc..eebe66cc 100644
--- a/PDP11/pdp11_ng.c
+++ b/PDP11/pdp11_ng.c
@@ -54,7 +54,7 @@ const char *ng_description (DEVICE *dptr);
 #define IOLN_NG   4
 DIB ng_dib = {
   IOBA_AUTO, IOLN_NG, &ng_rd, &ng_wr,
-  4, IVCL(NG), VEC_AUTO, {NULL}, IOLN_NG
+  1, IVCL(NG), VEC_AUTO, {NULL}, IOLN_NG
 };
 
 UNIT ng_unit = {