--- qtbase/src/widgets/widgets/qtabbar.cpp.orig	2019-03-19 12:24:14.000000000 -0400
+++ qtbase/src/widgets/widgets/qtabbar.cpp	2019-03-19 12:23:40.000000000 -0400
@@ -738,6 +738,8 @@
 {
     Q_Q(QTabBar);
     Q_ASSERT(index >= 0);
+    // play it safe
+    if (index < 0) return;
 
     Tab &tab = tabList[index];
     bool vertical = verticalTabs(shape);
