diff --git a/src/NCollection/NCollection_UBTree.hxx b/src/NCollection/NCollection_UBTree.hxx
index e39371a140..8074a78267 100644
--- a/src/NCollection/NCollection_UBTree.hxx
+++ b/src/NCollection/NCollection_UBTree.hxx
@@ -214,7 +214,7 @@ public:
      * This method should be used instead of operator delete.
      */ 
     static void delNode (TreeNode * theNode,
-                         Handle(NCollection_BaseAllocator)& theAlloc)
+                         const Handle(NCollection_BaseAllocator)& theAlloc)
     {
       if (theNode) {
         if (theNode -> myChildren) {