diff --git a/xo-allocutil/include/xo/allocutil/IAlloc.hpp b/xo-allocutil/include/xo/allocutil/IAlloc.hpp
index 703e968c..2c78b131 100644
--- a/xo-allocutil/include/xo/allocutil/IAlloc.hpp
+++ b/xo-allocutil/include/xo/allocutil/IAlloc.hpp
@@ -140,6 +140,12 @@ namespace xo {
              *  in-progress collection phase
              **/
             virtual bool check_move(IObject * /*src*/) const { return false; }
+            /** check write barrier (if impl has write barrier)
+             *  given an object @p parent that contains object pointer @p lhs.
+             **/
+            virtual bool check_write_barrier(IObject * /*parent*/,
+                                             IObject ** /*lhs*/,
+                                             bool /*may_throw*/) const { return true; };
             /** write barrier for collector.  perform assignment
              *    @code
              *    *lhs = rhs
diff --git a/xo-ordinaltree/include/xo/ordinaltree/RedBlackTree.hpp b/xo-ordinaltree/include/xo/ordinaltree/RedBlackTree.hpp
index 6e1fba07..78b1555b 100644
--- a/xo-ordinaltree/include/xo/ordinaltree/RedBlackTree.hpp
+++ b/xo-ordinaltree/include/xo/ordinaltree/RedBlackTree.hpp
@@ -534,15 +534,26 @@ namespace xo {
                     log("pre", xtag("key", key), xtag("tree", *this));
                 }
 
+                RbNode * adj_root = this->root_;
+
                 bool retval = RbUtil::erase_aux(this->node_alloc_,
                                                 key,
                                                 this->reduce_fn_,
                                                 debug_flag_,
-                                                &(this->root_));
+                                                &adj_root);
 
-                if (retval)
+                if (retval) {
                     --(this->size_);
 
+                    if (adj_root != root_) {
+                        allocator_type alloc = node_alloc_;
+
+                        this->_gc_assign_member(&(this->root_), adj_root, alloc);
+                    }
+                } else {
+                    assert(adj_root == root_);
+                }
+
                 if (log) {
                     log("post", xtag("tree", *this));
                 }
diff --git a/xo-ordinaltree/include/xo/ordinaltree/rbtree/Node.hpp b/xo-ordinaltree/include/xo/ordinaltree/rbtree/Node.hpp
index 27048041..f568c92c 100644
--- a/xo-ordinaltree/include/xo/ordinaltree/rbtree/Node.hpp
+++ b/xo-ordinaltree/include/xo/ordinaltree/rbtree/Node.hpp
@@ -266,8 +266,8 @@ namespace xo {
                 /* true if this node is red,  and either child is red */
                 bool is_red_violation() const {
                     if (this->color_ == C_Red) {
-                        Node *left = this->left_child();
-                        Node *right = this->right_child();
+                        Node *  left = this->left_child();
+                        Node * right = this->right_child();
 
                         if (left && left->is_red())
                             return true;
@@ -455,7 +455,7 @@ namespace xo {
                  */
                 std::pair<ReducedValue, ReducedValue> reduced_;
                 /* pointer to parent node,  nullptr iff this is the root node */
-                Node *parent_ = nullptr;
+                Node * parent_ = nullptr;
                 /*
                  * .child_v[0] = left child
                  * .child_v[1] = right child
diff --git a/xo-ordinaltree/include/xo/ordinaltree/rbtree/RbTreeUtil.hpp b/xo-ordinaltree/include/xo/ordinaltree/rbtree/RbTreeUtil.hpp
index 0545965a..f263b7b4 100644
--- a/xo-ordinaltree/include/xo/ordinaltree/rbtree/RbTreeUtil.hpp
+++ b/xo-ordinaltree/include/xo/ordinaltree/rbtree/RbTreeUtil.hpp
@@ -317,7 +317,7 @@ namespace xo {
                  */
                 static RbNode * find_rightmost(RbNode *N) {
                     while(N) {
-                        RbNode *S = N->right_child();
+                        RbNode * S = N->right_child();
 
                         if (!S)
                             break;
@@ -417,7 +417,7 @@ namespace xo {
                             return x;
                         }
 
-                        RbNode *y = find_lub(x->left_child(), k, is_closed);
+                        RbNode * y = find_lub(x->left_child(), k, is_closed);
 
                         if (y) {
                             /* found better upper bound in left subtree */
@@ -911,7 +911,7 @@ namespace xo {
 
                         assert(pp_root);
 
-                        RbNode *P = N->parent();
+                        RbNode * P = N->parent();
 
                         if (!P) {
                             /* N was the root node,  tree now empty */
@@ -948,9 +948,9 @@ namespace xo {
                          *       C   D
                          */
                         Direction other_d;
-                        RbNode *S = nullptr;
-                        RbNode *C = nullptr;
-                        RbNode *D = nullptr;
+                        RbNode * S = nullptr;
+                        RbNode * C = nullptr;
+                        RbNode * D = nullptr;
 
                         /* table of outcomes as a function of node color
                          *