diff --git a/libctru/include/3ds/util/rbtree.h b/libctru/include/3ds/util/rbtree.h
index 08778b9..5b27892 100644
--- a/libctru/include/3ds/util/rbtree.h
+++ b/libctru/include/3ds/util/rbtree.h
@@ -4,6 +4,7 @@
  */
 #pragma once
 
+#include <3ds/synchronization.h>
 #include <stdint.h>
 #include <stddef.h>
 
@@ -21,16 +22,21 @@ typedef int  (*rbtree_node_comparator_t)(const rbtree_node_t *lhs,
 /// An rbtree node.
 struct rbtree_node
 {
-  uintptr_t      parent_color; ///< Parent color.
-  rbtree_node_t  *child[2];    ///< Node children.
+  char          nodeTag[4];   ///< Node tag.
+  uintptr_t     parent_color; ///< Parent color.
+  rbtree_node_t *child[2];    ///< Node children.
+  rbtree_t      *tree;        ///< Owning tree.
 };
 
 /// An rbtree.
 struct rbtree
 {
+  char                     treeTag[4]; ///< Tree tag.
   rbtree_node_t            *root;      ///< Root node.
   rbtree_node_comparator_t comparator; ///< Node comparator.
   size_t                   size;       ///< Size.
+  LightLock                lock;       ///< Tree mutex.
+  bool                     busy;       ///< Busy flag.
 };
 
 #ifdef __cplusplus
diff --git a/libctru/source/util/rbtree/rbtree_clear.c b/libctru/source/util/rbtree/rbtree_clear.c
index fe5c803..084e947 100644
--- a/libctru/source/util/rbtree/rbtree_clear.c
+++ b/libctru/source/util/rbtree/rbtree_clear.c
@@ -5,27 +5,28 @@ void
 rbtree_clear(rbtree_t                 *tree,
              rbtree_node_destructor_t destructor)
 {
+  rbtree_set_busy(tree);
   rbtree_validate(tree);
 
   rbtree_node_t *node = tree->root;
 
-  while(tree->root != NULL)
+  while(tree->root)
   {
-    while(node->child[LEFT] != NULL)
+    while(node->child[LEFT])
       node = node->child[LEFT];
 
-    if(node->child[RIGHT] != NULL)
+    if(node->child[RIGHT])
       node = node->child[RIGHT];
     else
     {
       rbtree_node_t *parent = get_parent(node);
 
-      if(parent == NULL)
+      if(!parent)
         tree->root = NULL;
       else
         parent->child[node != parent->child[LEFT]] = NULL;
 
-      if(destructor != NULL)
+      if(destructor)
         (*destructor)(node);
 
       node = parent;
@@ -35,4 +36,5 @@ rbtree_clear(rbtree_t                 *tree,
   tree->size = 0;
 
   rbtree_validate(tree);
+  rbtree_clear_busy(tree);
 }
diff --git a/libctru/source/util/rbtree/rbtree_empty.c b/libctru/source/util/rbtree/rbtree_empty.c
index c47170d..4f592ba 100644
--- a/libctru/source/util/rbtree/rbtree_empty.c
+++ b/libctru/source/util/rbtree/rbtree_empty.c
@@ -4,7 +4,11 @@
 int
 rbtree_empty(const rbtree_t *tree)
 {
+  rbtree_set_busy((rbtree_t*)tree);
   rbtree_validate(tree);
 
-  return tree->root == NULL;
+  bool empty = !tree->root;
+
+  rbtree_clear_busy((rbtree_t*)tree);
+  return empty;
 }
diff --git a/libctru/source/util/rbtree/rbtree_find.c b/libctru/source/util/rbtree/rbtree_find.c
index 19c9f27..d6d3c8b 100644
--- a/libctru/source/util/rbtree/rbtree_find.c
+++ b/libctru/source/util/rbtree/rbtree_find.c
@@ -5,12 +5,13 @@ rbtree_node_t*
 rbtree_find(const rbtree_t      *tree,
             const rbtree_node_t *node)
 {
+  rbtree_set_busy((rbtree_t*)tree);
   rbtree_validate(tree);
 
   rbtree_node_t *tmp  = tree->root;
   rbtree_node_t *save = NULL;
 
-  while(tmp != NULL)
+  while(tmp)
   {
     int rc = (*tree->comparator)(node, tmp);
     if(rc < 0)
@@ -29,6 +30,7 @@ rbtree_find(const rbtree_t      *tree,
   }
 
   rbtree_validate(tree);
+  rbtree_clear_busy((rbtree_t*)tree);
 
   return save;
 }
diff --git a/libctru/source/util/rbtree/rbtree_init.c b/libctru/source/util/rbtree/rbtree_init.c
index b1a826c..f66f0ea 100644
--- a/libctru/source/util/rbtree/rbtree_init.c
+++ b/libctru/source/util/rbtree/rbtree_init.c
@@ -5,9 +5,15 @@ void
 rbtree_init(rbtree_t                 *tree,
             rbtree_node_comparator_t comparator)
 {
+  tree->treeTag[3] = 'T';
+  tree->treeTag[2] = 'R';
+  tree->treeTag[1] = 'E';
+  tree->treeTag[0] = 'E';
   tree->root       = NULL;
   tree->comparator = comparator;
   tree->size       = 0;
+  tree->busy       = false;
+  LightLock_Init(&tree->lock);
 
   rbtree_validate(tree);
 }
diff --git a/libctru/source/util/rbtree/rbtree_insert.c b/libctru/source/util/rbtree/rbtree_insert.c
index 536b9d2..56943fb 100644
--- a/libctru/source/util/rbtree/rbtree_insert.c
+++ b/libctru/source/util/rbtree/rbtree_insert.c
@@ -6,14 +6,24 @@ do_insert(rbtree_t      *tree,
           rbtree_node_t *node,
           int           multi)
 {
+  rbtree_set_busy(tree);
   rbtree_validate(tree);
 
+  node->nodeTag[3]   = 'N';
+  node->nodeTag[2]   = 'O';
+  node->nodeTag[1]   = 'D';
+  node->nodeTag[0]   = 'E';
+  node->parent_color = 0;
+  node->child[LEFT]  = NULL;
+  node->child[RIGHT] = NULL;
+  node->tree         = tree;
+
   rbtree_node_t *original = node;
   rbtree_node_t **tmp     = &tree->root;
   rbtree_node_t *parent   = NULL;
   rbtree_node_t *save     = NULL;
 
-  while(*tmp != NULL)
+  while(*tmp)
   {
     int cmp = (*(tree->comparator))(node, *tmp);
     parent  = *tmp;
@@ -31,9 +41,19 @@ do_insert(rbtree_t      *tree,
     }
   }
 
-  if(save != NULL)
+  if(save)
   {
+    node->nodeTag[3]   = 'D';
+    node->nodeTag[2]   = 'O';
+    node->nodeTag[1]   = 'N';
+    node->nodeTag[0]   = 'E';
+    node->parent_color = 0;
+    node->child[LEFT]  = NULL;
+    node->child[RIGHT] = NULL;
+    node->tree         = NULL;
+
     rbtree_validate(tree);
+    rbtree_clear_busy(tree);
 
     return save;
   }
@@ -83,6 +103,7 @@ do_insert(rbtree_t      *tree,
   tree->size += 1;
 
   rbtree_validate(tree);
+  rbtree_clear_busy(tree);
 
   return original;
 }
diff --git a/libctru/source/util/rbtree/rbtree_internal.h b/libctru/source/util/rbtree/rbtree_internal.h
index 8719afe..b0376f4 100644
--- a/libctru/source/util/rbtree/rbtree_internal.h
+++ b/libctru/source/util/rbtree/rbtree_internal.h
@@ -29,7 +29,7 @@ set_red(rbtree_node_t *node)
 static inline rbtree_color_t
 get_color(const rbtree_node_t *node)
 {
-  if(node == NULL)
+  if(!node)
     return BLACK;
   return (rbtree_color_t)(node->parent_color & COLOR_MASK);
 }
@@ -59,6 +59,12 @@ set_parent(rbtree_node_t       *node,
   node->parent_color = (get_color(node)) | ((uintptr_t)parent);
 }
 
+void
+rbtree_set_busy(rbtree_t *tree);
+
+void
+rbtree_clear_busy(rbtree_t *tree);
+
 void
 rbtree_rotate(rbtree_t      *tree,
               rbtree_node_t *node,
diff --git a/libctru/source/util/rbtree/rbtree_iterator.c b/libctru/source/util/rbtree/rbtree_iterator.c
index 424658d..a577d93 100644
--- a/libctru/source/util/rbtree/rbtree_iterator.c
+++ b/libctru/source/util/rbtree/rbtree_iterator.c
@@ -7,16 +7,16 @@ do_iterate(const rbtree_node_t *node,
 {
   rbtree_node_t *it = (rbtree_node_t*)node;
 
-  if(it->child[next] != NULL)
+  if(it->child[next])
   {
     it = it->child[next];
-    while(it->child[!next] != NULL)
+    while(it->child[!next])
       it = it->child[!next];
   }
   else
   {
     rbtree_node_t *parent = get_parent(node);
-    while(parent != NULL && it == parent->child[next])
+    while(parent && it == parent->child[next])
     {
       it = parent;
       parent = get_parent(it);
diff --git a/libctru/source/util/rbtree/rbtree_minmax.c b/libctru/source/util/rbtree/rbtree_minmax.c
index 54c9cf4..5455cca 100644
--- a/libctru/source/util/rbtree/rbtree_minmax.c
+++ b/libctru/source/util/rbtree/rbtree_minmax.c
@@ -5,35 +5,32 @@ static inline rbtree_node_t*
 do_minmax(const rbtree_t *tree,
           int            max)
 {
+  rbtree_set_busy((rbtree_t*)tree);
   rbtree_validate(tree);
 
   rbtree_node_t *node = tree->root;
 
-  if(node == NULL)
+  if(!node)
+  {
+    rbtree_clear_busy((rbtree_t*)tree);
     return NULL;
+  }
 
-  while(node->child[max] != NULL)
+  while(node->child[max])
     node = node->child[max];
 
+  rbtree_clear_busy((rbtree_t*)tree);
   return node;
 }
 
 rbtree_node_t*
 rbtree_min(const rbtree_t *tree)
 {
-  rbtree_node_t *node;
-
-  node = do_minmax(tree, LEFT);
-
-  return node;
+  return do_minmax(tree, LEFT);
 }
 
 rbtree_node_t*
 rbtree_max(const rbtree_t *tree)
 {
-  rbtree_node_t *node;
-
-  node = do_minmax(tree, RIGHT);
-
-  return node;
+  return do_minmax(tree, RIGHT);
 }
diff --git a/libctru/source/util/rbtree/rbtree_remove.c b/libctru/source/util/rbtree/rbtree_remove.c
index 412474c..2de1cbd 100644
--- a/libctru/source/util/rbtree/rbtree_remove.c
+++ b/libctru/source/util/rbtree/rbtree_remove.c
@@ -51,15 +51,37 @@ recolor(rbtree_t      *tree,
     }
   }
 
-  if(node != NULL)
+  if(node)
     set_black(node);
 }
 
+static bool
+in_tree(const rbtree_t      *tree,
+        const rbtree_node_t *node)
+{
+  if(tree->root == node)
+    return true;
+
+  const rbtree_node_t *parent = get_parent(node);
+  while(parent)
+  {
+    if(tree->root == parent)
+      return true;
+
+    parent = get_parent(parent);
+  }
+
+  return false;
+}
+
 rbtree_node_t*
 rbtree_remove(rbtree_t                 *tree,
               rbtree_node_t            *node,
               rbtree_node_destructor_t destructor)
 {
+  rbtree_set_busy(tree);
+  if(!in_tree(tree, node))
+    svcBreak(USERBREAK_PANIC);
   rbtree_validate(tree);
 
   rbtree_color_t color;
@@ -68,16 +90,16 @@ rbtree_remove(rbtree_t                 *tree,
 
   next = rbtree_node_next(node);
 
-  if(node->child[LEFT] != NULL && node->child[RIGHT] != NULL)
+  if(node->child[LEFT] && node->child[RIGHT])
   {
     rbtree_node_t *old = node;
 
     node = node->child[RIGHT];
-    while(node->child[LEFT] != NULL)
+    while(node->child[LEFT])
       node = node->child[LEFT];
 
     parent = get_parent(old);
-    if(parent != NULL)
+    if(parent)
     {
       if(parent->child[LEFT] == old)
         parent->child[LEFT] = node;
@@ -95,7 +117,7 @@ rbtree_remove(rbtree_t                 *tree,
       parent = node;
     else
     {
-      if(child != NULL)
+      if(child)
         set_parent(child, parent);
       parent->child[LEFT] = child;
 
@@ -109,7 +131,7 @@ rbtree_remove(rbtree_t                 *tree,
   }
   else
   {
-    if(node->child[LEFT] == NULL)
+    if(!node->child[LEFT])
       child = node->child[RIGHT];
     else
       child = node->child[LEFT];
@@ -117,9 +139,9 @@ rbtree_remove(rbtree_t                 *tree,
     parent = get_parent(node);
     color  = get_color(node);
 
-    if(child != NULL)
+    if(child)
       set_parent(child, parent);
-    if(parent != NULL)
+    if(parent)
     {
       if(parent->child[LEFT] == node)
         parent->child[LEFT] = child;
@@ -133,12 +155,22 @@ rbtree_remove(rbtree_t                 *tree,
   if(color == BLACK)
     recolor(tree, parent, child);
 
-  if(destructor != NULL)
+  original->nodeTag[3]   = 'D';
+  original->nodeTag[2]   = 'O';
+  original->nodeTag[1]   = 'N';
+  original->nodeTag[0]   = 'E';
+  original->parent_color = 0;
+  original->child[LEFT]  = NULL;
+  original->child[RIGHT] = NULL;
+  original->tree         = NULL;
+
+  if(destructor)
     (*destructor)(original);
 
   tree->size -= 1;
 
   rbtree_validate(tree);
+  rbtree_clear_busy(tree);
 
   return next;
 }
diff --git a/libctru/source/util/rbtree/rbtree_rotate.c b/libctru/source/util/rbtree/rbtree_rotate.c
index c47d290..4897a04 100644
--- a/libctru/source/util/rbtree/rbtree_rotate.c
+++ b/libctru/source/util/rbtree/rbtree_rotate.c
@@ -10,12 +10,12 @@ rbtree_rotate(rbtree_t      *tree,
   rbtree_node_t *parent = get_parent(node);
 
   node->child[left] = tmp->child[!left];
-  if(tmp->child[!left] != NULL)
+  if(tmp->child[!left])
     set_parent(tmp->child[!left], node);
 
   tmp->child[!left] = node;
   set_parent(tmp, parent);
-  if(parent != NULL)
+  if(parent)
   {
     if(node == parent->child[!left])
       parent->child[!left] = tmp;
diff --git a/libctru/source/util/rbtree/rbtree_size.c b/libctru/source/util/rbtree/rbtree_size.c
index e596366..5bc35ad 100644
--- a/libctru/source/util/rbtree/rbtree_size.c
+++ b/libctru/source/util/rbtree/rbtree_size.c
@@ -4,7 +4,11 @@
 size_t
 rbtree_size(const rbtree_t *tree)
 {
+  rbtree_set_busy((rbtree_t*)tree);
   rbtree_validate(tree);
 
-  return tree->size;
+  size_t size = tree->size;
+
+  rbtree_clear_busy((rbtree_t*)tree);
+  return size;
 }
diff --git a/libctru/source/util/rbtree/rbtree_validate.c b/libctru/source/util/rbtree/rbtree_validate.c
index 431635e..281b06c 100644
--- a/libctru/source/util/rbtree/rbtree_validate.c
+++ b/libctru/source/util/rbtree/rbtree_validate.c
@@ -9,7 +9,6 @@
   abort(); \
 } while(0)
 
-
 void
 rbtree_validate(const rbtree_t *tree)
 {
@@ -23,7 +22,7 @@ rbtree_validate(const rbtree_t *tree)
   // root node's parent must be null
   if(tree->root)
   {
-    if(get_parent(tree->root) != NULL)
+    if(get_parent(tree->root))
       panic();
   }
 
@@ -42,7 +41,7 @@ rbtree_node_validate(const rbtree_t *tree, const rbtree_node_t *node, size_t *si
   if(!node) // implies is_black
   {
     if(black)
-      *black += 1;
+      *black = 1;
 
     if(depth)
       *depth = 1;
@@ -108,14 +107,14 @@ rbtree_node_validate(const rbtree_t *tree, const rbtree_node_t *node, size_t *si
 
   // size is left+right subtrees plus self
   if(size)
-    *size += left_size + right_size + 1;
+    *size = left_size + right_size + 1;
 
   // all possible paths to leaf nodes must have the same number of black nodes along the path
   if(left_black != right_black)
     panic();
 
   if(black)
-    *black += left_black + (is_black(node) ? 1 : 0);
+    *black = left_black + (is_black(node) ? 1 : 0);
 
   // depth of one subtree must not exceed 2x depth of the other subtree
   if(left_depth < right_depth)
@@ -134,3 +133,25 @@ rbtree_node_validate(const rbtree_t *tree, const rbtree_node_t *node, size_t *si
       *depth = right_depth + 1;
   }
 }
+
+void
+rbtree_set_busy(rbtree_t *tree)
+{
+  LightLock_Lock(&tree->lock);
+  if(tree->busy)
+    panic();
+
+  tree->busy = true;
+  LightLock_Unlock(&tree->lock);
+}
+
+void
+rbtree_clear_busy(rbtree_t *tree)
+{
+  LightLock_Lock(&tree->lock);
+  if(!tree->busy)
+    panic();
+
+  tree->busy = false;
+  LightLock_Unlock(&tree->lock);
+}
diff --git a/libctru/source/util/rbtree/test/main.cpp b/libctru/source/util/rbtree/test/main.cpp
index 3799e1b..ed45f06 100644
--- a/libctru/source/util/rbtree/test/main.cpp
+++ b/libctru/source/util/rbtree/test/main.cpp
@@ -111,7 +111,8 @@ int main(int argc, char *argv[])
       else
         nodes.emplace_back(node);
 
-      if(remove() < chance)
+      // remove random node
+      if(remove() <= chance)
       {
         auto it = std::begin(nodes) + (eng() % nodes.size());
         rbtree_remove(&tree, &(*it)->node, IntNodeDestructor);
@@ -122,5 +123,7 @@ int main(int argc, char *argv[])
     }
   }
 
+  std::printf("Ended with %zu nodes in tree\n", rbtree_size(&tree));
+
   rbtree_clear(&tree, IntNodeDestructor);
 }