diff --git a/map/src/map.hpp b/map/src/map.hpp
index 1aaa76a..a6794b6 100644
--- a/map/src/map.hpp
+++ b/map/src/map.hpp
@@ -263,6 +263,82 @@ class map {
         path_of_successor = node;
       }
     }
+    void DeleteFixUp(RedBlackTreeNodeType *&tree_root) {
+      assert(this->left == nullptr && this->right == nullptr);
+      assert(this->color == RedBlackTreeColorType::BLACK);
+      RedBlackTreeNodeType *sibling = GetSibling();
+      assert(sibling != nullptr);
+      if (sibling->color == RedBlackTreeColorType::RED) {
+        // Case 1
+        parent->color = RedBlackTreeColorType::RED;
+        sibling->color = RedBlackTreeColorType::BLACK;
+        if (this == parent->left) {
+          parent->RotateLeft(tree_root);
+        } else {
+          parent->RotateRight(tree_root);
+        }
+        this->DeleteFixUp(tree_root);
+        return;
+      }
+      RedBlackTreeNodeType *close_nephew = nullptr;
+      RedBlackTreeNodeType *distant_nephew = nullptr;
+      if (this == parent->left) {
+        close_nephew = sibling->left;
+        distant_nephew = sibling->right;
+      } else {
+        close_nephew = sibling->right;
+        distant_nephew = sibling->left;
+      }
+      if (sibling->color == RedBlackTreeColorType::BLACK && this->parent->color == RedBlackTreeColorType::RED &&
+          (close_nephew == nullptr || close_nephew != nullptr && close_nephew->color == RedBlackTreeColorType::BLACK) &&
+          (distant_nephew == nullptr ||
+           distant_nephew != nullptr && distant_nephew->color == RedBlackTreeColorType::BLACK)) {
+        // Case 2
+        assert(close_nephew == nullptr);
+        assert(distant_nephew == nullptr);
+        sibling->color = RedBlackTreeColorType::RED;
+        this->parent->color = RedBlackTreeColorType::BLACK;
+        return;
+      }
+      if (sibling->color == RedBlackTreeColorType::BLACK && this->parent->color == RedBlackTreeColorType::BLACK &&
+          (close_nephew == nullptr || close_nephew != nullptr && close_nephew->color == RedBlackTreeColorType::BLACK) &&
+          (distant_nephew == nullptr ||
+           distant_nephew != nullptr && distant_nephew->color == RedBlackTreeColorType::BLACK)) {
+        // Case 3
+        assert(close_nephew == nullptr);
+        assert(distant_nephew == nullptr);
+        sibling->color = RedBlackTreeColorType::RED;
+        this->parent->DeleteFixUp(tree_root);
+        return;
+      }
+      if (close_nephew != nullptr && close_nephew->color == RedBlackTreeColorType::RED) {
+        // Case 4
+        if (this == parent->left) {
+          sibling->color = RedBlackTreeColorType::RED;
+          close_nephew->color = RedBlackTreeColorType::BLACK;
+          sibling->RotateRight(tree_root);
+        } else {
+          sibling->color = RedBlackTreeColorType::RED;
+          close_nephew->color = RedBlackTreeColorType::BLACK;
+          sibling->RotateLeft(tree_root);
+        }
+        this->DeleteFixUp(tree_root);
+        return;
+      }
+      assert(distant_nephew != nullptr && distant_nephew->color == RedBlackTreeColorType::RED);
+      // Then it must be Case 5
+      if (this == parent->left) {
+        sibling->color = parent->color;
+        parent->color = RedBlackTreeColorType::BLACK;
+        distant_nephew->color = RedBlackTreeColorType::BLACK;
+        parent->RotateLeft(tree_root);
+      } else {
+        sibling->color = parent->color;
+        parent->color = RedBlackTreeColorType::BLACK;
+        distant_nephew->color = RedBlackTreeColorType::BLACK;
+        parent->RotateRight(tree_root);
+      }
+    }
     static void DeleteNode(RedBlackTreeNodeType *pos, RedBlackTreeNodeType *&tree_root) {
       if (pos->parent == nullptr && pos->left == nullptr && pos->right == nullptr) {
         // Case 0: The only node in the tree.
@@ -280,11 +356,12 @@ class map {
       }
       if (pos->left == nullptr && pos->right == nullptr) {
         // Case 2
-        if (pos->color == RedBlackTreeColorType::RED) {
-          pos->GetSelfPath(tree_root) = nullptr;
-          delete pos;
-          return;
+        if (pos->color == RedBlackTreeColorType::BLACK) {
+          pos->DeleteFixUp(tree_root);
         }
+        pos->GetSelfPath(tree_root) = nullptr;
+        delete pos;
+        return;
       }
       // Case 3
       RedBlackTreeNodeType *replacement = (pos->left != nullptr ? pos->left : pos->right);
@@ -295,16 +372,16 @@ class map {
       replacement->color = RedBlackTreeColorType::BLACK;
       delete pos;
     }
+    static void CopyFrom(RedBlackTreeNodeType *&target, const RedBlackTreeNodeType *source) {
+      if (source == nullptr) return;
+      target = new RedBlackTreeNodeType(source->val, nullptr, nullptr, nullptr, source->color);
+      CopyFrom(target->left, source->left);
+      CopyFrom(target->right, source->right);
+      target->SetChildrensParent();
+    }
   };
   size_t node_count;
   RedBlackTreeNodeType *tree_root;
-  void CopyFrom(RedBlackTreeNodeType *&target, const RedBlackTreeNodeType *source) {
-    if (source == nullptr) return;
-    target = new RedBlackTreeNodeType(source->val, nullptr, nullptr, nullptr, source->color);
-    CopyFrom(target->left, source->left);
-    CopyFrom(target->right, source->right);
-    target->SetChildrensParent();
-  }
 
  public:
   /**
@@ -497,7 +574,7 @@ class map {
   map() : node_count(0), tree_root(nullptr) {}
   map(const map &other) {
     node_count = other.node_count;
-    CopyFrom(tree_root, other.tree_root);
+    RedBlackTreeNodeType::CopyFrom(tree_root, other.tree_root);
   }
   map(map &&other) {
     node_count = other.node_count;
@@ -513,7 +590,7 @@ class map {
     if (tree_root) tree_root->ReleaseAll();
     delete tree_root;
     node_count = other.node_count;
-    CopyFrom(tree_root, other.tree_root);
+    RedBlackTreeNodeType::CopyFrom(tree_root, other.tree_root);
     return *this;
   }
   map &operator=(map &&other) {