diff --git a/gtsam/base/serializationTestHelpers.h b/gtsam/base/serializationTestHelpers.h
index 4ef09beb1..06b3462e9 100644
--- a/gtsam/base/serializationTestHelpers.h
+++ b/gtsam/base/serializationTestHelpers.h
@@ -19,6 +19,7 @@
 
 #pragma once
 
+#include <iostream>
 #include <sstream>
 #include <string>