diff --git a/dynamic_programming/longest_increasing_subsequence_nlogn.cpp b/dynamic_programming/longest_increasing_subsequence_nlogn.cpp
index 5bc72345c..5c4ecfc49 100644
--- a/dynamic_programming/longest_increasing_subsequence_nlogn.cpp
+++ b/dynamic_programming/longest_increasing_subsequence_nlogn.cpp
@@ -3,6 +3,7 @@
 // tested on : https://cses.fi/problemset/task/1145/
 
 #include <iostream>
+#include <set>
 
 using namespace std;
 int LIS(int arr[], int n) {