diff --git a/VAX/vax610_sysdev.c b/VAX/vax610_sysdev.c
index b37a6cee..c4099ddc 100644
--- a/VAX/vax610_sysdev.c
+++ b/VAX/vax610_sysdev.c
@@ -363,6 +363,8 @@ t_stat vax610_boot (int32 flag, CONST char *ptr)
 {
 t_stat r;
 
+if ((ptr = get_sim_sw (ptr)) == NULL)                   /* get switches */
+    return SCPE_INVSW;
 r = vax610_boot_parse (flag, ptr);                      /* parse the boot cmd */
 if (r != SCPE_OK) {                                     /* error? */
     if (r >= SCPE_BASE) {                               /* message available? */
diff --git a/VAX/vax630_sysdev.c b/VAX/vax630_sysdev.c
index f6b72b94..3d16a1ac 100644
--- a/VAX/vax630_sysdev.c
+++ b/VAX/vax630_sysdev.c
@@ -905,6 +905,8 @@ t_stat vax630_boot (int32 flag, CONST char *ptr)
 {
 char gbuf[CBUFSIZE];
 
+if ((ptr = get_sim_sw (ptr)) == NULL)               /* get switches */
+    return SCPE_INVSW;
 get_glyph (ptr, gbuf, 0);                           /* get glyph */
 if (gbuf[0] && strcmp (gbuf, "CPU"))
     return SCPE_ARG;                                /* Only can specify CPU device */
diff --git a/VAX/vax730_sys.c b/VAX/vax730_sys.c
index 0353d8e4..0059a951 100644
--- a/VAX/vax730_sys.c
+++ b/VAX/vax730_sys.c
@@ -470,6 +470,8 @@ t_stat vax730_boot (int32 flag, CONST char *ptr)
 {
 t_stat r;
 
+if ((ptr = get_sim_sw (ptr)) == NULL)                   /* get switches */
+    return SCPE_INVSW;
 r = vax730_boot_parse (flag, ptr);                      /* parse the boot cmd */
 if (r != SCPE_OK) {                                     /* error? */
     if (r >= SCPE_BASE) {                               /* message available? */
diff --git a/VAX/vax750_cmi.c b/VAX/vax750_cmi.c
index 3dc60dfa..bfc0ab00 100644
--- a/VAX/vax750_cmi.c
+++ b/VAX/vax750_cmi.c
@@ -609,6 +609,8 @@ t_stat vax750_boot (int32 flag, CONST char *ptr)
 {
 t_stat r;
 
+if ((ptr = get_sim_sw (ptr)) == NULL)                   /* get switches */
+    return SCPE_INVSW;
 r = vax750_boot_parse (flag, ptr);                      /* parse the boot cmd */
 if (r != SCPE_OK) {                                     /* error? */
     if (r >= SCPE_BASE) {                               /* message available? */
diff --git a/VAX/vax780_sbi.c b/VAX/vax780_sbi.c
index 1ab5b6be..9453909a 100644
--- a/VAX/vax780_sbi.c
+++ b/VAX/vax780_sbi.c
@@ -650,6 +650,8 @@ t_stat r;
 
 if (!ptr || !*ptr)
     return SCPE_2FARG;
+if ((ptr = get_sim_sw (ptr)) == NULL)                   /* get switches */
+    return SCPE_INVSW;
 regptr = get_glyph (ptr, gbuf, 0);                      /* get glyph */
 if ((slptr = strchr (gbuf, '/'))) {                     /* found slash? */
     regptr = strchr (ptr, '/');                         /* locate orig */
diff --git a/VAX/vax860_abus.c b/VAX/vax860_abus.c
index b8667575..e190a105 100644
--- a/VAX/vax860_abus.c
+++ b/VAX/vax860_abus.c
@@ -686,6 +686,8 @@ t_stat vax860_boot (int32 flag, CONST char *ptr)
 {
 t_stat r;
 
+if ((ptr = get_sim_sw (ptr)) == NULL)                   /* get switches */
+    return SCPE_INVSW;
 r = vax860_boot_parse (flag, ptr);                      /* parse the boot cmd */
 if (r != SCPE_OK) {                                     /* error? */
     if (r >= SCPE_BASE) {                               /* message available? */
diff --git a/VAX/vax_sysdev.c b/VAX/vax_sysdev.c
index 252ca143..46d24fa3 100644
--- a/VAX/vax_sysdev.c
+++ b/VAX/vax_sysdev.c
@@ -1704,6 +1704,8 @@ t_stat vax_boot (int32 flag, CONST char *ptr)
 {
 char gbuf[CBUFSIZE];
 
+if ((ptr = get_sim_sw (ptr)) == NULL)               /* get switches */
+    return SCPE_INVSW;
 get_glyph (ptr, gbuf, 0);                           /* get glyph */
 if (gbuf[0] && strcmp (gbuf, "CPU"))
     return SCPE_ARG;                                /* Only can specify CPU device */