diff --git a/constants.h b/constants.h
index a22b98e..34013e8 100644
--- a/constants.h
+++ b/constants.h
@@ -66,6 +66,7 @@
 extern const char kPrefsPreviousVersion[];
 extern const char kPrefsResumedUpdateFailures[];
 extern const char kPrefsRollbackVersion[];
+extern const char kPrefsChannelOnSlotPrefix[];
 extern const char kPrefsSystemUpdatedMarker[];
 extern const char kPrefsTargetVersionAttempt[];
 extern const char kPrefsTargetVersionInstalledFrom[];