diff --git a/src/environment.cpp b/src/environment.cpp
index c7e114d..d79e689 100644
--- a/src/environment.cpp
+++ b/src/environment.cpp
@@ -1,3 +1,4 @@
+#include <iostream>
 #include <array>
 #include <vector>
 #include <math.h>
diff --git a/src/particle.cpp b/src/particle.cpp
index cd46b00..f53cba3 100644
--- a/src/particle.cpp
+++ b/src/particle.cpp
@@ -1,3 +1,4 @@
+#include <iostream>
 #include <array>
 
 #include "../include/particle.h"