diff --git a/src/face.cpp b/src/face.cpp
index 1161192..45d577b 100644
--- a/src/face.cpp
+++ b/src/face.cpp
@@ -10,8 +10,8 @@
 using namespace std;
 
 namespace ndn {
-  
-uint64_t 
+
+const PendingInterestId*
 Face::expressInterest
   (const Name& name, const Interest *interestTemplate, const OnData& onData, const OnTimeout& onTimeout)
 {