diff --git a/numerical_methods/fast_fourier_transform.cpp b/numerical_methods/fast_fourier_transform.cpp
index 5ecaa5d3d..a54731216 100644
--- a/numerical_methods/fast_fourier_transform.cpp
+++ b/numerical_methods/fast_fourier_transform.cpp
@@ -14,7 +14,7 @@
 #include<cmath>     /// for mathematical-related functions
 #include<complex>  /// for storing points and coefficents
 #include <cassert> /// for assert
-#include<vector>
+#include<vector>   /// for storing test cases