diff --git a/app/vmalert/notifier/alert.go b/app/vmalert/notifier/alert.go
index 3bdd3a8f85..2dd13ec925 100644
--- a/app/vmalert/notifier/alert.go
+++ b/app/vmalert/notifier/alert.go
@@ -191,7 +191,7 @@ func (a Alert) toPromLabels(relabelCfg *promrelabel.ParsedConfigs) []prompbmarsh
 	var labels []prompbmarshal.Label
 	for k, v := range a.Labels {
 		labels = append(labels, prompbmarshal.Label{
-			Name:  k,
+			Name:  promrelabel.SanitizeMetricName(k),
 			Value: v,
 		})
 	}
diff --git a/app/vmalert/notifier/alert_test.go b/app/vmalert/notifier/alert_test.go
index bff5359968..c2a51c3042 100644
--- a/app/vmalert/notifier/alert_test.go
+++ b/app/vmalert/notifier/alert_test.go
@@ -237,6 +237,11 @@ func TestAlert_toPromLabels(t *testing.T) {
 		[]prompbmarshal.Label{{Name: "a", Value: "baz"}, {Name: "foo", Value: "bar"}},
 		nil,
 	)
+	fn(
+		map[string]string{"foo.bar": "baz", "service!name": "qux"},
+		[]prompbmarshal.Label{{Name: "foo_bar", Value: "baz"}, {Name: "service_name", Value: "qux"}},
+		nil,
+	)
 
 	pcs, err := promrelabel.ParseRelabelConfigsData([]byte(`
 - target_label: "foo"
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 8cd6171215..830ea7cda7 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -17,6 +17,7 @@ The following `tip` changes can be tested by building VictoriaMetrics components
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): prevent from `FATAL: cannot flush metainfo` panic when [`-remoteWrite.multitenantURL`](https://docs.victoriametrics.com/vmagent.html#multitenancy) command-line flag is set. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5357).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): properly decode zstd-encoded data blocks received via [VictoriaMetrics remote_write protocol](https://docs.victoriametrics.com/vmagent.html#victoriametrics-remote-write-protocol). See [this issue comment](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5301#issuecomment-1815871992).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): properly add new labels at `output_relabel_configs` during [stream aggregation](https://docs.victoriametrics.com/stream-aggregation.html). Previously this could lead to corrupted labels in output samples. Thanks to @ChengChung for providing [detailed report for this bug](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5402).
+* BUGFIX: [vmalert](https://docs.victoriametrics.com/vmalert.html): sanitize label names before sending the alert notification to Alertmanager. Before, vmalert would send notifications with labels containing characters not supported by Alertmanager validator, resulting into validation errors like `msg="Failed to validate alerts" err="invalid label set: invalid name "foo.bar"`.
 * BUGFIX: properly escape `<` character in responses returned via [`/federate`](https://docs.victoriametrics.com/#federation) endpoint. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5431).
 
 ## [v1.93.8](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.93.8)