diff --git a/math/complex_numbers.cpp b/math/complex_numbers.cpp
index 9a381b125..4505b5677 100644
--- a/math/complex_numbers.cpp
+++ b/math/complex_numbers.cpp
@@ -9,6 +9,7 @@
 #include <cmath>
 #include <iostream>
 #include <stdexcept>
+#include <cassert>
 
 /**
  * Class Complex to represent complex numbers as a field.