diff --git a/gtsam/linear/LossFunctions.cpp b/gtsam/linear/LossFunctions.cpp
index 80b3e3312..2a82122cd 100644
--- a/gtsam/linear/LossFunctions.cpp
+++ b/gtsam/linear/LossFunctions.cpp
@@ -18,6 +18,8 @@
 
 #include <gtsam/linear/LossFunctions.h>
 
+#include <iostream>
+
 using namespace std;
 
 namespace gtsam {