diff --git a/ndn-cpp/encoding/der/der.cpp b/ndn-cpp/encoding/der/der.cpp
index 7981727..0b5531e 100644
--- a/ndn-cpp/encoding/der/der.cpp
+++ b/ndn-cpp/encoding/der/der.cpp
@@ -576,7 +576,7 @@
 /*
  * DerGtime
  */
-DerGtime::DerGtime(const Time& time)
+DerGtime::DerGtime(const MillisecondsSince1970& time)
   :DerNode(DER_GENERALIZED_TIME)
 {
   string pTimeStr = toIsoString(time);
@@ -594,14 +594,14 @@
 DerGtime::~DerGtime()
 {}
 
-string DerGtime::toIsoString(const Time& time)
+string DerGtime::toIsoString(const MillisecondsSince1970& time)
 {
 #if 1
   throw std::runtime_error("not implemented");
 #endif
 }
 
-Time DerGtime::fromIsoString(const string& isoString)
+MillisecondsSince1970 DerGtime::fromIsoString(const string& isoString)
 {
 #if 1
   throw std::runtime_error("not implemented");
diff --git a/ndn-cpp/encoding/der/der.hpp b/ndn-cpp/encoding/der/der.hpp
index 9ed4a2a..ff92c78 100644
--- a/ndn-cpp/encoding/der/der.hpp
+++ b/ndn-cpp/encoding/der/der.hpp
@@ -355,7 +355,7 @@
 class DerGtime : public DerNode
 {
 public:
-  DerGtime(const Time& time);
+  DerGtime(const MillisecondsSince1970& time);
 
   DerGtime(std::istream& start);
   
@@ -372,14 +372,14 @@
    * @param time Milliseconds since 1/1/1970.
    * @return The ISO string.
    */
-  static std::string toIsoString(const Time& time);
+  static std::string toIsoString(const MillisecondsSince1970& time);
   
   /**
    * Convert from the ISO string representation to the internal time format.
    * @param isoString The ISO time formatted string. 
    * @return The time in milliseconds since 1/1/1970.
    */
-  static Time fromIsoString(const std::string& isoString);
+  static MillisecondsSince1970 fromIsoString(const std::string& isoString);
 };
  
 } // der