diff --git a/gui/quadtree.h b/gui/quadtree.h
index d28e4e8f..f240f345 100644
--- a/gui/quadtree.h
+++ b/gui/quadtree.h
@@ -116,7 +116,7 @@ template <typename CoordinateT, typename ElementT> class QuadTreeNode
     BoundingBox bound_;
     // How many elements should be contained in this node until it splits into
     // sub-nodes.
-    const size_t max_elems_;
+    size_t max_elems_;
     // Four sub-nodes or nullptr if it hasn't split yet.
     std::unique_ptr<QuadTreeNode<CoordinateT, ElementT>[]> children_ = nullptr;
     // Coordinates of the split.