diff --git a/dbus_constants.h b/dbus_constants.h
index e4173f0..625ac8d 100644
--- a/dbus_constants.h
+++ b/dbus_constants.h
@@ -12,6 +12,12 @@
     "/org/chromium/UpdateEngine";
 static const char* const kUpdateEngineServiceInterface =
     "org.chromium.UpdateEngineInterface";
+
+// Flags used in the AttemptUpdateWithFlags() D-Bus method.
+typedef enum {
+  kAttemptUpdateFlagNonInteractive = (1<<0)
+} AttemptUpdateFlags;
+
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_DBUS_CONSTANTS_H__