diff --git a/src/security/identity-certificate.cpp b/src/security/identity-certificate.cpp
index d4b0d38..685fa29 100644
--- a/src/security/identity-certificate.cpp
+++ b/src/security/identity-certificate.cpp
@@ -25,10 +25,10 @@
 
 #include "identity-certificate.hpp"
 
-using namespace std;
-
 namespace ndn {
 
+using std::string;
+
 bool
 IdentityCertificate::isCorrectName(const Name& name)
 {