diff --git a/src/std/rec/mbbiDirectRecord.c b/src/std/rec/mbbiDirectRecord.c
index 74cc3d1f9..1d603ab5a 100644
--- a/src/std/rec/mbbiDirectRecord.c
+++ b/src/std/rec/mbbiDirectRecord.c
@@ -120,9 +120,9 @@ static long init_record(mbbiDirectRecord *prec, int pass)
     if (prec->siol.type == CONSTANT)
         recGblInitConstantLink(&prec->siol, DBF_USHORT, &prec->sval);
 
-    /* Initialize MASK if the user didn't */
-    if (prec->mask == 0)
-        prec->mask = (1 << prec->nobt) - 1;
+    /* Initialize MASK if the user set NOBT instead */
+    if (prec->mask == 0 && prec->nobt <= 32)
+        prec->mask = ((epicsUInt64) 1u << prec->nobt) - 1;
 
     if (pdset->init_record) {
         status = pdset->init_record(prec);
diff --git a/src/std/rec/mbbiRecord.c b/src/std/rec/mbbiRecord.c
index 9c1ec6fd1..bfc4fdba6 100644
--- a/src/std/rec/mbbiRecord.c
+++ b/src/std/rec/mbbiRecord.c
@@ -137,9 +137,9 @@ static long init_record(mbbiRecord *prec, int pass)
     if (prec->siol.type == CONSTANT)
         recGblInitConstantLink(&prec->siol, DBF_USHORT, &prec->sval);
 
-    /* Initialize MASK if the user didn't */
-    if (prec->mask == 0)
-        prec->mask = (1 << prec->nobt) - 1;
+    /* Initialize MASK if the user set NOBT instead */
+    if (prec->mask == 0 && prec->nobt <= 32)
+        prec->mask = ((epicsUInt64) 1u << prec->nobt) - 1;
 
     if (pdset->init_record)
         status = pdset->init_record(prec);
diff --git a/src/std/rec/mbbiRecord.dbd b/src/std/rec/mbbiRecord.dbd
index bbb9fd17a..ffc37cfaf 100644
--- a/src/std/rec/mbbiRecord.dbd
+++ b/src/std/rec/mbbiRecord.dbd
@@ -3,9 +3,8 @@
 #     National Laboratory.
 # Copyright (c) 2002 The Regents of the University of California, as
 #     Operator of Los Alamos National Laboratory.
-# EPICS BASE Versions 3.13.7
-# and higher are distributed subject to a Software License Agreement found
-# in file LICENSE that is included with this distribution. 
+# EPICS BASE is distributed subject to a Software License Agreement found
+# in file LICENSE that is included with this distribution.
 #*************************************************************************
 recordtype(mbbi) {
 	include "dbCommon.dbd" 
@@ -15,7 +14,7 @@ recordtype(mbbi) {
 		asl(ASL0)
 		pp(TRUE)
 	}
-	field(NOBT,DBF_SHORT) {
+	field(NOBT,DBF_USHORT) {
 		prompt("Number of Bits")
 		promptgroup(GUI_MBB)
 		special(SPC_NOMOD)
diff --git a/src/std/rec/mbboDirectRecord.c b/src/std/rec/mbboDirectRecord.c
index 728f99d74..ae43bdcf2 100644
--- a/src/std/rec/mbboDirectRecord.c
+++ b/src/std/rec/mbboDirectRecord.c
@@ -123,9 +123,9 @@ static long init_record(mbboDirectRecord *prec, int pass)
         if (recGblInitConstantLink(&prec->dol, DBF_USHORT, &prec->val))
             prec->udf = FALSE;
 
-    /* Initialize MASK if the user didn't */
-    if (prec->mask == 0)
-        prec->mask = (1 << prec->nobt) - 1;
+    /* Initialize MASK if the user set NOBT instead */
+    if (prec->mask == 0 && prec->nobt <= 32)
+        prec->mask = ((epicsUInt64) 1u << prec->nobt) - 1;
 
     if (pdset->init_record) {
         status = pdset->init_record(prec);
diff --git a/src/std/rec/mbboRecord.c b/src/std/rec/mbboRecord.c
index 4655638c4..ffb6f1eed 100644
--- a/src/std/rec/mbboRecord.c
+++ b/src/std/rec/mbboRecord.c
@@ -143,9 +143,9 @@ static long init_record(mbboRecord *prec, int pass)
         if (recGblInitConstantLink(&prec->dol, DBF_USHORT, &prec->val))
             prec->udf = FALSE;
 
-    /* Initialize MASK if the user didn't */
-    if (prec->mask == 0)
-        prec->mask = (1 << prec->nobt) - 1;
+    /* Initialize MASK if the user set NOBT instead */
+    if (prec->mask == 0 && prec->nobt <= 32)
+        prec->mask = ((epicsUInt64) 1u << prec->nobt) - 1;
 
     if (pdset->init_record) {
         status = pdset->init_record(prec);
diff --git a/src/std/rec/mbboRecord.dbd b/src/std/rec/mbboRecord.dbd
index 5920a0c76..1a32ad1cd 100644
--- a/src/std/rec/mbboRecord.dbd
+++ b/src/std/rec/mbboRecord.dbd
@@ -3,9 +3,8 @@
 #     National Laboratory.
 # Copyright (c) 2002 The Regents of the University of California, as
 #     Operator of Los Alamos National Laboratory.
-# EPICS BASE Versions 3.13.7
-# and higher are distributed subject to a Software License Agreement found
-# in file LICENSE that is included with this distribution. 
+# EPICS BASE is distributed subject to a Software License Agreement found
+# in file LICENSE that is included with this distribution.
 #*************************************************************************
 recordtype(mbbo) {
 	include "dbCommon.dbd" 
@@ -29,7 +28,7 @@ recordtype(mbbo) {
 		interest(1)
 		menu(menuOmsl)
 	}
-	field(NOBT,DBF_SHORT) {
+	field(NOBT,DBF_USHORT) {
 		prompt("Number of Bits")
 		promptgroup(GUI_MBB)
 		special(SPC_NOMOD)