diff --git a/docs/configuration/configuration.md b/docs/configuration/configuration.md
index 30bb07a8c1..0efded225d 100644
--- a/docs/configuration/configuration.md
+++ b/docs/configuration/configuration.md
@@ -3415,6 +3415,10 @@ static_configs:
 # List of Alertmanager relabel configurations.
 relabel_configs:
   [ - <relabel_config> ... ]
+
+# List of alert relabel configurations.
+alert_relabel_configs:
+  [ - <relabel_config> ... ]
 ```
 
 ### `<remote_write>`
diff --git a/notifier/notifier.go b/notifier/notifier.go
index 630cbdf1e5..0f93c25a35 100644
--- a/notifier/notifier.go
+++ b/notifier/notifier.go
@@ -383,13 +383,11 @@ func relabelAlerts(relabelConfigs []*relabel.Config, externalLabels labels.Label
 
 	for _, a := range alerts {
 		lb.Reset(a.Labels)
-		if externalLabels.Len() > 0 {
-			externalLabels.Range(func(l labels.Label) {
-				if a.Labels.Get(l.Name) == "" {
-					lb.Set(l.Name, l.Value)
-				}
-			})
-		}
+		externalLabels.Range(func(l labels.Label) {
+			if a.Labels.Get(l.Name) == "" {
+				lb.Set(l.Name, l.Value)
+			}
+		})
 
 		keep := relabel.ProcessBuilder(lb, relabelConfigs...)
 		if !keep {