--- /home/marxin/Programming/bison-3.0.4/tests/c++.at	2015-01-20 20:39:51.000000000 +0100
+++ tests/c++.at	2016-12-14 10:58:00.046437207 +0100
@@ -197,6 +197,10 @@
 #include <list>
 #include <string>
 typedef std::list<std::string> strings_type;
+namespace std
+{
+  std::ostream& operator<<(std::ostream& o, const strings_type& s);
+}
 }
 
 %code // code for the .cc file