diff --git a/apps/diameter_client/DiameterClient.cpp b/apps/diameter_client/DiameterClient.cpp
index f7bc40f3..715ed697 100644
--- a/apps/diameter_client/DiameterClient.cpp
+++ b/apps/diameter_client/DiameterClient.cpp
@@ -108,7 +108,7 @@ void DiameterClient::sendRequest(const AmArg& args,
   }
   conn_mut.unlock();
 
-  DBG("found %d active connections for application %s\n", 
+  DBG("found %zd active connections for application %s\n", 
       scs.size(), app_name.c_str());
 
   if (scs.empty()) {