diff --git a/metrics_constants.h b/metrics_constants.h
index eabb8fb..b3833a3 100644
--- a/metrics_constants.h
+++ b/metrics_constants.h
@@ -60,6 +60,10 @@
   // above block and before the kInputMalformed field. This
   // is to ensure that error codes are not reordered.
 
+  // This error is reported when libcurl has an internal error that
+  // update_engine can't recover from.
+  kInternalError = 99,
+
   // This error code is used to convey that malformed input was given
   // to the utils::GetDownloadErrorCode() function. This should never
   // happen but if it does it's because of an internal update_engine