diff --git a/ndn-cpp/security/certificate/certificate-extension.cpp b/ndn-cpp/security/certificate/certificate-extension.cpp
index aba88dd..d3719a7 100644
--- a/ndn-cpp/security/certificate/certificate-extension.cpp
+++ b/ndn-cpp/security/certificate/certificate-extension.cpp
@@ -20,6 +20,7 @@
 shared_ptr<der::DerNode> 
 CertificateExtension::toDer()
 {
+#if 0 // Include again when der is defined.
   shared_ptr<der::DerSequence> root(new der::DerSequence);
     
   shared_ptr<der::DerOid> extensionId(new der::DerOid(extensionId_));
@@ -33,6 +34,9 @@
   root->getSize();
 
   return root;
+#else
+  throw std::runtime_error("not implemented");
+#endif
 }
 
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