diff --git a/CHANGELOG.md b/CHANGELOG.md
index dee286e74c..2f7a8d9066 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#2033](https://github.com/thanos-io/thanos/pull/2033) minio-go: Fixed Issue #1494 support Web Identity providers for IAM credentials for AWS EKS
 - [#1985](https://github.com/thanos-io/thanos/pull/1985) store gateway: Fixed case where series entry is larger than 64KB in index.
 - [#2051](https://github.com/thanos-io/thanos/pull/2051) ruler: Fixed issue where ruler does not expose shipper metrics.
+- [#2101](https://github.com/thanos-io/thanos/pull/2101) ruler: Fixed bug where thanos_alert_sender_errors_total was not registered.
 
 ### Added
 
diff --git a/pkg/alert/alert.go b/pkg/alert/alert.go
index 7cb11a75bd..418cb5c831 100644
--- a/pkg/alert/alert.go
+++ b/pkg/alert/alert.go
@@ -313,7 +313,7 @@ func NewSender(
 		}, []string{"alertmanager"}),
 	}
 	if reg != nil {
-		reg.MustRegister(s.sent, s.dropped, s.latency)
+		reg.MustRegister(s.sent, s.errs, s.dropped, s.latency)
 	}
 	return s
 }