diff --git a/prefs_interface.h b/prefs_interface.h
index dbfa68a..724651e 100644
--- a/prefs_interface.h
+++ b/prefs_interface.h
@@ -9,6 +9,7 @@
 
 namespace chromeos_update_engine {
 
+extern const char kPrefsDeltaUpdateFailures[];
 extern const char kPrefsLastActivePingDay[];
 extern const char kPrefsLastRollCallPingDay[];