diff --git a/constants.h b/constants.h
index e97ec90..4bd9685 100644
--- a/constants.h
+++ b/constants.h
@@ -33,6 +33,7 @@
 extern const char kPrefsLastRollCallPingDay[];
 extern const char kPrefsManifestMetadataSize[];
 extern const char kPrefsNumReboots[];
+extern const char kPrefsNumResponsesSeen[];
 extern const char kPrefsPayloadAttemptNumber[];
 extern const char kPrefsPreviousVersion[];
 extern const char kPrefsResumedUpdateFailures[];