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>
diff --git a/tools/ndncert-ca-status.cpp b/tools/ndncert-ca-status.cpp
index 09fd64a..a55812e 100644
--- a/tools/ndncert-ca-status.cpp
+++ b/tools/ndncert-ca-status.cpp
@@ -21,6 +21,8 @@
 #include "ca-module.hpp"
 #include "ca-detail/ca-sqlite.hpp"
 
+#include <iostream>
+
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/variables_map.hpp>
 #include <boost/program_options/parsers.hpp>
diff --git a/tools/ndncert-client.cpp b/tools/ndncert-client.cpp
index 86ff60f..7f082d8 100644
--- a/tools/ndncert-client.cpp
+++ b/tools/ndncert-client.cpp
@@ -22,6 +22,8 @@
 #include "challenge-module.hpp"
 #include "logging.hpp"
 
+#include <iostream>
+
 #include <boost/program_options/options_description.hpp>
 #include <boost/program_options/variables_map.hpp>
 #include <boost/program_options/parsers.hpp>