diff --git a/pkg/alertmanager/alertmanager.go b/pkg/alertmanager/alertmanager.go
index 7d5ef579952..3b7b35a5770 100644
--- a/pkg/alertmanager/alertmanager.go
+++ b/pkg/alertmanager/alertmanager.go
@@ -519,6 +519,7 @@ func (am *Alertmanager) ApplyConfig(conf *definition.PostableApiAlertingConfig,
 
 	am.templatesMtx.Lock()
 	am.templates = tmpls
+	am.tmplExternalURL = tmplExternalURL
 	am.templatesMtx.Unlock()
 
 	pipeline := am.pipelineBuilder.New(