diff --git a/src/util/shared-constants.hpp b/src/util/shared-constants.hpp
index e29491e..1e710b2 100644
--- a/src/util/shared-constants.hpp
+++ b/src/util/shared-constants.hpp
@@ -18,6 +18,8 @@
 *
 * See AUTHORS for complete list of nTorrent authors and contributors.
 */
+#ifndef INCLUDED_SHARED_CONSTANTS_HPP
+#define INCLUDED_SHARED_CONSTANTS_HPP
 
 namespace ndn {
 namespace ntorrent {
@@ -28,3 +30,5 @@
 
 } // namespace ntorrent
 } // namespace ndn
+
+#endif
\ No newline at end of file