diff --git a/src/ndncert-common.hpp b/src/ndncert-common.hpp
index d052d62..a9165a2 100644
--- a/src/ndncert-common.hpp
+++ b/src/ndncert-common.hpp
@@ -155,6 +155,8 @@
 
 std::string requestTypeToString(RequestType type);
 
+std::string errorCodeToString(ErrorCode code);
+
 typedef boost::property_tree::ptree JsonSection;
 
 std::string