diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index ede5c36d73f..dc80a4b81f7 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -3388,6 +3388,7 @@ void QHeaderViewPrivate::setDefaultSectionSize(int size)
     sectionStartposRecalc = true;
     if (hasAutoResizeSections())
         doDelayedResizeSections();
+    viewport->update();
 }
 
 void QHeaderViewPrivate::recalcSectionStartPos() const // linear (but fast)