diff --git a/src/sync-validator.cc b/src/sync-validator.cc
index e1d40d8..f2c05bb 100644
--- a/src/sync-validator.cc
+++ b/src/sync-validator.cc
@@ -14,12 +14,13 @@
 #include <queue>
 
 using namespace ndn;
-using namespace std;
 
 INIT_LOGGER ("SyncValidator");
 
 namespace Sync {
 
+using ndn::shared_ptr;
+
 const shared_ptr<CertificateCache> SyncValidator::DefaultCertificateCache = shared_ptr<CertificateCache>();
 const shared_ptr<SecRuleRelative> SyncValidator::DefaultDataRule = shared_ptr<SecRuleRelative>();
 
@@ -56,7 +57,7 @@
 void
 SyncValidator::deriveTrustNodes()
 {
-  queue<Name> nodeQueue;
+  std::queue<Name> nodeQueue;
 
   // Clear existing trust nodes.
   m_trustedNodes.clear();
@@ -151,7 +152,7 @@
       catch(SignatureSha256WithRsa::Error& e)
         {
           return onValidationFailed(data.shared_from_this(), 
-                                    "Not SignatureSha256WithRsa signature: " + string(e.what()));
+                                    "Not SignatureSha256WithRsa signature: " + std::string(e.what()));
         }
       catch(KeyLocator::Error& e)
         {
@@ -194,13 +195,13 @@
   catch(IntroCertificate::Error& e)
     {
       return onValidationFailed(data, 
-                                "Intro cert decoding error: " + string(e.what()));
+                                "Intro cert decoding error: " + std::string(e.what()));
     }
 }
 
 void
 SyncValidator::onCertificateValidationFailed(const shared_ptr<const Data>& signCertificate, 
-                                             const string& failureInfo,
+                                             const std::string& failureInfo,
                                              const shared_ptr<const Data>& data, 
                                              const OnDataValidationFailed& onValidationFailed)
 {
@@ -223,7 +224,7 @@
 }
 
 void
-SyncValidator::onCertRegisterFailed(const Name& prefix, const string& msg)
+SyncValidator::onCertRegisterFailed(const Name& prefix, const std::string& msg)
 {
   _LOG_DEBUG("SyncValidator::onCertRegisterFailed: " << msg);
 }