diff --git a/tools/ndnsec/key-gen.cpp b/tools/ndnsec/key-gen.cpp
index 1d3d79a..553f06c 100644
--- a/tools/ndnsec/key-gen.cpp
+++ b/tools/ndnsec/key-gen.cpp
@@ -22,6 +22,8 @@
 #include "ndnsec.hpp"
 #include "util.hpp"
 
+#include "ndn-cxx/util/io.hpp"
+
 namespace ndn {
 namespace ndnsec {