diff --git a/src/net/dns/host_cache.cc b/src/net/dns/host_cache.cc
index 74c9588333..50f54bb23f 100644
--- a/src/net/dns/host_cache.cc
+++ b/src/net/dns/host_cache.cc
@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <string>
 #include <vector>
+#include <unordered_set>
 
 #include "base/bind.h"
 #include "base/metrics/field_trial.h"