diff --git a/src/main/java/org/dataalgorithms/bonus/friendrecommendation/mapreduce/PairOfLongs.java b/src/main/java/org/dataalgorithms/bonus/friendrecommendation/mapreduce/PairOfLongs.java
index 1285aef7..861bce15 100644
--- a/src/main/java/org/dataalgorithms/bonus/friendrecommendation/mapreduce/PairOfLongs.java
+++ b/src/main/java/org/dataalgorithms/bonus/friendrecommendation/mapreduce/PairOfLongs.java
@@ -95,6 +95,10 @@ public void set(long left, long right) {
     *         otherwise
     */
    public boolean equals(Object obj) {
+     if (obj == null)
+        return false;
+     if (this.getClass() != obj.getClass())
+        return false;  
      PairOfLongs pair = (PairOfLongs) obj;
      return left == pair.getLeft() && right == pair.getRight();
    }
diff --git a/src/main/java/org/dataalgorithms/chap05/mapreduce/PairOfWords.java b/src/main/java/org/dataalgorithms/chap05/mapreduce/PairOfWords.java
index 103f5c28..7e960b41 100755
--- a/src/main/java/org/dataalgorithms/chap05/mapreduce/PairOfWords.java
+++ b/src/main/java/org/dataalgorithms/chap05/mapreduce/PairOfWords.java
@@ -146,6 +146,10 @@ public void set(String left, String right) {
 	 * @return <code>true</code> if <code>obj</code> is equal to this object, <code>false</code> otherwise
 	 */
 	public boolean equals(Object obj) {
+		if (obj == null)
+			return false;
+		if (this.getClass() != obj.getClass())
+			return false;
 		PairOfWords pair = (PairOfWords) obj;
 		return leftElement.equals(pair.getLeftElement())
 				&& rightElement.equals(pair.getRightElement());