diff --git a/src/widgets/widgets/qbuttongroup.cpp b/src/widgets/widgets/qbuttongroup.cpp
index 079ef45e907..db89b137b55 100644
--- a/src/widgets/widgets/qbuttongroup.cpp
+++ b/src/widgets/widgets/qbuttongroup.cpp
@@ -211,12 +211,11 @@ void QButtonGroup::addButton(QAbstractButton *button, int id)
     button->d_func()->group = this;
     d->buttonList.append(button);
     if (id == -1) {
-        const QHash<QAbstractButton*, int>::const_iterator it
-                = std::min_element(d->mapping.cbegin(), d->mapping.cend());
+        const auto it = std::min_element(d->mapping.cbegin(), d->mapping.cend());
         if (it == d->mapping.cend())
             d->mapping[button] = -2;
         else
-            d->mapping[button] = *it - 1;
+            d->mapping[button] = (*it >= 0) ? -2 : (*it - 1);
     } else {
         d->mapping[button] = id;
     }
diff --git a/tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp b/tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp
index 566f4ed52ce..a1d27ed4a55 100644
--- a/tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp
+++ b/tests/auto/widgets/widgets/qbuttongroup/tst_qbuttongroup.cpp
@@ -539,18 +539,18 @@ void tst_QButtonGroup::autoIncrementId()
     QRadioButton *radio3 = new QRadioButton(&dlg);
     radio3->setText("radio3");
 
-    buttons->addButton(radio1);
+    buttons->addButton(radio1, 2);
     vbox->addWidget(radio1);
-    buttons->addButton(radio2);
+    buttons->addButton(radio2, -1);
     vbox->addWidget(radio2);
     buttons->addButton(radio3);
     vbox->addWidget(radio3);
 
     radio1->setChecked(true);
 
-    QCOMPARE(buttons->id(radio1), -2);
-    QCOMPARE(buttons->id(radio2), -3);
-    QCOMPARE(buttons->id(radio3), -4);
+    QCOMPARE(buttons->id(radio1), 2);
+    QCOMPARE(buttons->id(radio2), -2);
+    QCOMPARE(buttons->id(radio3), -3);
 
     dlg.show();
 }