diff --git a/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp b/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
index 1f4c3d1c18..1c4653d522 100644
--- a/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
+++ b/src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp
@@ -601,7 +601,7 @@ QList<QGraphicsItem *> QGraphicsSceneBspTreeIndex::items(Qt::SortOrder order) co
     10 items.
 
 */
-int QGraphicsSceneBspTreeIndex::bspTreeDepth()
+int QGraphicsSceneBspTreeIndex::bspTreeDepth() const
 {
     Q_D(const QGraphicsSceneBspTreeIndex);
     return d->bspTreeDepth;
diff --git a/src/widgets/graphicsview/qgraphicsscenebsptreeindex_p.h b/src/widgets/graphicsview/qgraphicsscenebsptreeindex_p.h
index d1b3099295..b3b31fca6a 100644
--- a/src/widgets/graphicsview/qgraphicsscenebsptreeindex_p.h
+++ b/src/widgets/graphicsview/qgraphicsscenebsptreeindex_p.h
@@ -83,7 +83,7 @@ public:
     QList<QGraphicsItem *> estimateTopLevelItems(const QRectF &rect, Qt::SortOrder order) const;
     QList<QGraphicsItem *> items(Qt::SortOrder order = Qt::DescendingOrder) const;
 
-    int bspTreeDepth();
+    int bspTreeDepth() const;
     void setBspTreeDepth(int depth);
 
 protected Q_SLOTS: