diff --git a/tools/ndncert-ca-server.cpp b/tools/ndncert-ca-server.cpp
index e61f5b5..c757d45 100644
--- a/tools/ndncert-ca-server.cpp
+++ b/tools/ndncert-ca-server.cpp
@@ -20,6 +20,8 @@
 
 #include "ca-module.hpp"
 
+#include <iostream>
+
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/variables_map.hpp>
 #include <boost/program_options/parsers.hpp>