diff --git a/ndn-cpp/util/changed-event.cpp b/ndn-cpp/util/changed-event.cpp
index 1d12c75..63b4569 100644
--- a/ndn-cpp/util/changed-event.cpp
+++ b/ndn-cpp/util/changed-event.cpp
@@ -13,7 +13,7 @@
 void 
 ChangedEvent::fire()
 {
-  for (unsigned int i = 0; i < listeners_.size(); ++i)
+  for (size_t i = 0; i < listeners_.size(); ++i)
     listeners_[i]();
 }