diff --git a/VAX/vax410_sysdev.c b/VAX/vax410_sysdev.c
index b07c67a1..98a3dc82 100644
--- a/VAX/vax410_sysdev.c
+++ b/VAX/vax410_sysdev.c
@@ -891,7 +891,7 @@ ka_mser = 0;
 ka_mear = 0;
 ka_cfgtst = (CFGT_TYP | CFGT_CUR);
 if (MEMSIZE > (1u << 21))                               /* more than 2MB? */
-    ka_cfgtst |= ((MEMSIZE >> 21) & CFGT_MEM);
+    ka_cfgtst |= (((MEMSIZE - (1u << 21)) >> 21) & CFGT_MEM);
 if ((vc_dev.flags & DEV_DIS) == 0)                      /* mono video enabled? */
     ka_cfgtst &= ~CFGT_TYP;
 if ((va_dev.flags & DEV_DIS) == 0) {                    /* video option present? */