diff --git a/core/face-monitor.hpp b/core/face-monitor.hpp
index 28cfdbd..459b181 100644
--- a/core/face-monitor.hpp
+++ b/core/face-monitor.hpp
@@ -32,7 +32,7 @@
 
 namespace ndn {
 class Face;
-struct PendingInterestId;
+class PendingInterestId;
 }
 
 namespace nfd {