diff --git a/src/widgets/widgets/qspinbox.cpp b/src/widgets/widgets/qspinbox.cpp
index 6ac2e1cec29..e504d7f5357 100644
--- a/src/widgets/widgets/qspinbox.cpp
+++ b/src/widgets/widgets/qspinbox.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2020 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtWidgets module of the Qt Toolkit.
@@ -1281,9 +1281,10 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
     const bool minus = min <= 0;
 
     const QString group(locale.groupSeparator());
-    const uint groupUcs = (group.size() > 1 && group.at(0).isHighSurrogate()
-                           ? QChar::surrogateToUcs4(group.at(0), group.at(1))
-                           : group.at(0).unicode());
+    const uint groupUcs = (group.isEmpty() ? 0 :
+                           (group.size() > 1 && group.at(0).isHighSurrogate()
+                            ? QChar::surrogateToUcs4(group.at(0), group.at(1))
+                            : group.at(0).unicode()));
     switch (len) {
     case 0:
         state = max != min ? QValidator::Intermediate : QValidator::Invalid;
@@ -1306,7 +1307,7 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
     default: break;
     }
 
-    if (copy.at(0) == locale.groupSeparator()) {
+    if (groupUcs && copy.startsWith(group)) {
         QSBDEBUG() << __FILE__ << __LINE__<< "state is set to Invalid";
         state = QValidator::Invalid;
         goto end;
@@ -1322,8 +1323,9 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
                 state = QValidator::Invalid;
                 goto end;
             }
-            for (int i=dec + 1; i<copy.size(); ++i) {
-                if (copy.at(i).isSpace() || copy.at(i) == locale.groupSeparator()) {
+            for (int i = dec + 1; i < copy.size(); ++i) {
+                if (copy.at(i).isSpace()
+                    || (groupUcs && QStringView{copy}.sliced(i).startsWith(group))) {
                     QSBDEBUG() << __FILE__ << __LINE__<< "state is set to Invalid";
                     state = QValidator::Invalid;
                     goto end;
@@ -1331,10 +1333,11 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
             }
         } else {
             const QChar last = copy.back();
-            const bool groupEnd = copy.endsWith(group);
+            const bool groupEnd = groupUcs && copy.endsWith(group);
             const QStringView head(copy.constData(), groupEnd ? len - group.size() : len - 1);
             const QChar secondLast = head.back();
-            if ((groupEnd || last.isSpace()) && (head.endsWith(group) || secondLast.isSpace())) {
+            if ((groupEnd || last.isSpace())
+                && ((groupUcs && head.endsWith(group)) || secondLast.isSpace())) {
                 state = QValidator::Invalid;
                 QSBDEBUG() << __FILE__ << __LINE__<< "state is set to Invalid";
                 goto end;
@@ -1353,7 +1356,7 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
 
         if (!ok) {
             if (QChar::isPrint(groupUcs)) {
-                if (max < 1000 && min > -1000 && copy.contains(group)) {
+                if (max < 1000 && min > -1000 && groupUcs && copy.contains(group)) {
                     state = QValidator::Invalid;
                     QSBDEBUG() << __FILE__ << __LINE__<< "state is set to Invalid";
                     goto end;
@@ -1361,7 +1364,7 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
 
                 const int len = copy.size();
                 for (int i = 0; i < len - 1;) {
-                    if (QStringView(copy).mid(i).startsWith(group)) {
+                    if (groupUcs && QStringView{copy}.sliced(i).startsWith(group)) {
                         if (QStringView(copy).mid(i + group.size()).startsWith(group)) {
                             QSBDEBUG() << __FILE__ << __LINE__<< "state is set to Invalid";
                             state = QValidator::Invalid;
@@ -1374,7 +1377,8 @@ QVariant QDoubleSpinBoxPrivate::validateAndInterpret(QString &input, int &pos,
                 }
 
                 QString copy2 = copy;
-                copy2.remove(group);
+                if (groupUcs)
+                    copy2.remove(group);
                 num = locale.toDouble(copy2, &ok);
                 QSBDEBUG() << group << num << copy2 << ok;