diff --git a/build/pdp10-ka/gt40 b/build/pdp10-ka/gt40
index 9823605c..55760f7a 100644
--- a/build/pdp10-ka/gt40
+++ b/build/pdp10-ka/gt40
@@ -22,6 +22,7 @@ set vt enable
 set vt crt=vr14
 set vt scale=1
 set vt address=17772000
+set vt vec=320
 set rom enabled
 set rom0 address=17766000
 at rom0 out/pdp10-ka/bootvt.img