diff --git a/dhcp_provider.cc b/dhcp_provider.cc
index bbf73fb..035484e 100644
--- a/dhcp_provider.cc
+++ b/dhcp_provider.cc
@@ -36,7 +36,7 @@
 
 DHCPConfigRefPtr DHCPProvider::GetConfig(int pid) {
   VLOG(2) << __func__;
-  PIDConfigMap::iterator it = configs_.find(pid);
+  PIDConfigMap::const_iterator it = configs_.find(pid);
   if (it == configs_.end()) {
     return NULL;
   }