--- a/utsushi/string.hpp	2020-05-08 23:20:11.642359134 +0200
+++ b/utsushi/string.hpp	2020-05-08 23:20:21.834246187 +0200
@@ -23,6 +23,7 @@
 
 #include <iosfwd>
 #include <string>
+#include <iostream>
 
 #include <boost/operators.hpp>
 
--- a/utsushi/toggle.hpp	2019-11-18 03:08:06.000000000 +0100
+++ b/utsushi/toggle.hpp	2020-05-08 23:23:40.284045167 +0200
@@ -22,6 +22,7 @@
 #define utsushi_toggle_hpp_
 
 #include <iosfwd>
+#include <iostream>
 #include <boost/operators.hpp>
 
 namespace utsushi {