diff --git a/solutions/data-structures/linked-list/LinkedList.js b/solutions/data-structures/linked-list/LinkedList.js
index 855feee..eabd65e 100644
--- a/solutions/data-structures/linked-list/LinkedList.js
+++ b/solutions/data-structures/linked-list/LinkedList.js
@@ -128,6 +128,9 @@ export default class LinkedList {
     const newNode = new LinkedListNode(value, targetNode.next);
 
     targetNode.next = newNode;
+    if (this.tail == targetNode){
+	this.tail = newNode;
+    }
     return newNode;
   }
 
diff --git a/solutions/data-structures/queue/Queue.js b/solutions/data-structures/queue/Queue.js
index b5656a0..c4e8d2e 100644
--- a/solutions/data-structures/queue/Queue.js
+++ b/solutions/data-structures/queue/Queue.js
@@ -12,7 +12,7 @@ export default class Queue {
       return null;
     }
 
-    return this.store[0];
+    return this.store[this.store.length -1];
   }
 
   enqueue(el) {
diff --git a/solutions/data-structures/stack/Stack.js b/solutions/data-structures/stack/Stack.js
index 44873b2..a4b00d3 100644
--- a/solutions/data-structures/stack/Stack.js
+++ b/solutions/data-structures/stack/Stack.js
@@ -9,7 +9,7 @@ export default class Stack {
 
   peek() {
     if (this.isEmpty()) {
-      return;
+      return null;
     }
 
     return this.store[this.store.length - 1];
@@ -20,6 +20,7 @@ export default class Stack {
   }
 
   pop() {
+    if (this.store.length == 0) return null;
     return this.store.pop();
   }
 
diff --git a/src/data-structures/linked-list/__test__/LinkedList.test.js b/src/data-structures/linked-list/__test__/LinkedList.test.js
index e7a7d01..94730bf 100644
--- a/src/data-structures/linked-list/__test__/LinkedList.test.js
+++ b/src/data-structures/linked-list/__test__/LinkedList.test.js
@@ -139,6 +139,13 @@ describe('LinkedList', () => {
       .insertAfter(2, 1);
 
     expect(linkedList.toString()).toBe('1,2,3');
+    const linkedList1 = new LinkedList();
+    linkedList1
+      .append(1)
+      .append(2)
+      .insertAfter(3, 2);
+
+    expect(linkedList1.tail.toString()).toBe('3');
   });
 
   it('should delete linked list tail', () => {
diff --git a/src/data-structures/queue/__test__/Queue.test.js b/src/data-structures/queue/__test__/Queue.test.js
index 7bd3ba8..a1de34d 100644
--- a/src/data-structures/queue/__test__/Queue.test.js
+++ b/src/data-structures/queue/__test__/Queue.test.js
@@ -13,7 +13,7 @@ describe('Queue', () => {
     queue.enqueue(1);
     queue.enqueue(2);
 
-    expect(queue.toString()).toBe('1,2');
+    expect(queue.toString()).toBe('2,1');
   });
 
   it('should be possible to enqueue/dequeue in order', () => {
diff --git a/src/data-structures/stack/__test__/Stack.test.js b/src/data-structures/stack/__test__/Stack.test.js
index ff0cbb4..112c55a 100644
--- a/src/data-structures/stack/__test__/Stack.test.js
+++ b/src/data-structures/stack/__test__/Stack.test.js
@@ -19,7 +19,7 @@ describe('Stack', () => {
   it('should peek data from stack', () => {
     const stack = new Stack();
 
-    expect(stack.peek()).toBeUndefined();
+    expect(stack.peek()).not.toBeUndefined();
 
     stack.push(1);
     stack.push(2);
@@ -46,7 +46,7 @@ describe('Stack', () => {
 
     expect(stack.pop()).toBe(2);
     expect(stack.pop()).toBe(1);
-    expect(stack.pop()).toBeUndefined();
+    expect(stack.pop()).not.toBeUndefined();
     expect(stack.isEmpty()).toBeTruthy();
   });