diff --git a/libcxx/include/__tree b/libcxx/include/__tree
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -147,6 +147,7 @@
 _NodePtr
 __tree_min(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "Root node shouldn't be null");
     while (__x->__left_ != nullptr)
         __x = __x->__left_;
     return __x;
@@ -159,6 +160,7 @@
 _NodePtr
 __tree_max(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "Root node shouldn't be null");
     while (__x->__right_ != nullptr)
         __x = __x->__right_;
     return __x;
@@ -170,6 +172,7 @@
 _NodePtr
 __tree_next(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
     if (__x->__right_ != nullptr)
         return _VSTD::__tree_min(__x->__right_);
     while (!_VSTD::__tree_is_left_child(__x))
@@ -182,6 +185,7 @@
 _EndNodePtr
 __tree_next_iter(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
     if (__x->__right_ != nullptr)
         return static_cast<_EndNodePtr>(_VSTD::__tree_min(__x->__right_));
     while (!_VSTD::__tree_is_left_child(__x))
@@ -197,6 +201,7 @@
 _NodePtr
 __tree_prev_iter(_EndNodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
     if (__x->__left_ != nullptr)
         return _VSTD::__tree_max(__x->__left_);
     _NodePtr __xx = static_cast<_NodePtr>(__x);
@@ -211,6 +216,7 @@
 _NodePtr
 __tree_leaf(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
     while (true)
     {
         if (__x->__left_ != nullptr)
@@ -235,6 +241,8 @@
 void
 __tree_left_rotate(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
+    _LIBCPP_ASSERT(__x->__right_ != nullptr, "node should have a right child");
     _NodePtr __y = __x->__right_;
     __x->__right_ = __y->__left_;
     if (__x->__right_ != nullptr)
@@ -255,6 +263,8 @@
 void
 __tree_right_rotate(_NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__x != nullptr, "node shouldn't be null");
+    _LIBCPP_ASSERT(__x->__left_ != nullptr, "node should have a left child");
     _NodePtr __y = __x->__left_;
     __x->__left_ = __y->__right_;
     if (__x->__left_ != nullptr)
@@ -269,7 +279,7 @@
 }
 
 // Effects:  Rebalances __root after attaching __x to a leaf.
-// Precondition:  __root != nulptr && __x != nullptr.
+// Precondition:  __root != nullptr && __x != nullptr.
 //                __x has no children.
 //                __x == __root or == a direct or indirect child of __root.
 //                If __x were to be unlinked from __root (setting __root to
@@ -280,6 +290,8 @@
 void
 __tree_balance_after_insert(_NodePtr __root, _NodePtr __x) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__root != nullptr, "Root of the tree shouldn't be null");
+    _LIBCPP_ASSERT(__x != nullptr, "Can't attach null node to a leaf");
     __x->__is_black_ = __x == __root;
     while (__x != __root && !__x->__parent_unsafe()->__is_black_)
     {
@@ -350,6 +362,8 @@
 void
 __tree_remove(_NodePtr __root, _NodePtr __z) _NOEXCEPT
 {
+    _LIBCPP_ASSERT(__root != nullptr, "Root node should not be null");
+    _LIBCPP_ASSERT(__z != nullptr, "The node to remove should not be null");
     // __z will be removed from the tree.  Client still needs to destruct/deallocate it
     // __y is either __z, or if __z has two children, __tree_next(__z).
     // __y will have at most one child.