diff --git a/mock_modem_gsm_network_proxy.h b/mock_modem_gsm_network_proxy.h
index 219ace1..8108d02 100644
--- a/mock_modem_gsm_network_proxy.h
+++ b/mock_modem_gsm_network_proxy.h
@@ -5,6 +5,8 @@
 #ifndef SHILL_MOCK_MODEM_GSM_NETWORK_PROXY_H_
 #define SHILL_MOCK_MODEM_GSM_NETWORK_PROXY_H_
 
+#include <string>
+
 #include <base/basictypes.h>
 #include <gmock/gmock.h>