diff --git a/TreeItem.cc b/TreeItem.cc
index eeaa919ae9c772aad1fd29d8c30ed1b39511d509..3f9861bd754f333c842e443f25d35629e78e8018 100644
--- a/TreeItem.cc
+++ b/TreeItem.cc
@@ -42,8 +42,6 @@
 
 #include "TreeItem.hh"
 
-/// Acceleration map
-static QMap<int,TreeItem*> treeMap_;
 
 //--------------------------------------------------------------------------------
 
@@ -191,8 +189,9 @@ TreeItem* TreeItem::next() {
     while ( parentPointer ) {
 
       // If there is an unvisited child of the parent, return this one
-      if ( parentPointer->childCount() > ( thisPointer->row() + 1) ) {
-        return parentPointer->childItems_[ thisPointer->row() + 1 ];
+      const int position = (thisPointer->row() + 1);
+      if ( parentPointer->childCount() > ( position ) ) {
+        return parentPointer->childItems_[ position ];
       }
 
       // Go to the next level
diff --git a/TreeItem.hh b/TreeItem.hh
index 112cd9b7a8b6393582f76d13b37c0f308fb273e5..4297aa354f30d20bb7dfee51c65a92aeeea265f3 100644
--- a/TreeItem.hh
+++ b/TreeItem.hh
@@ -110,12 +110,15 @@ class TreeItem {
     int level();
 
   private:
-    /// Parent item or 0 if rootnode
+    /// Parent item or 0 if root node
     TreeItem *parentItem_;
 
     /// Children of this node
     QList<TreeItem*> childItems_;
 
+    /// Acceleration map
+    static QMap<int,TreeItem*> treeMap_;
+
   public:
     //===========================================================================
     /** @name Tree : Parent nodes
@@ -125,7 +128,7 @@ class TreeItem {
     /// get the row of this item from the parent
     int row() const;
 
-    /// Get the parent item ( 0 if rootitem )
+    /// Get the parent item ( 0 if root item )
     TreeItem *parent();
 
     /// Set the parent pointer