diff --git a/common/constants.h b/common/constants.h
index 67519bd..248fd05 100644
--- a/common/constants.h
+++ b/common/constants.h
@@ -19,6 +19,9 @@
 
 namespace chromeos_update_engine {
 
+// The root path of all exclusion prefs.
+extern const char kExclusionPrefsSubDir[];
+
 // The root path of all DLC metadata.
 extern const char kDlcPrefsSubDir[];