diff --git a/src/xspice/icm/digital/d_process/ifspec.ifs b/src/xspice/icm/digital/d_process/ifspec.ifs
index d1502a8d7..07da5123c 100644
--- a/src/xspice/icm/digital/d_process/ifspec.ifs
+++ b/src/xspice/icm/digital/d_process/ifspec.ifs
@@ -47,7 +47,7 @@ Default_Type:        d              d
 Allowed_Types:       [d]            [d]
 Vector:              no             yes
 Vector_Bounds:       -              [1 -]
-Null_Allowed:        yes            yes
+Null_Allowed:        yes            no