diff --git a/model/relabel/relabel_test.go b/model/relabel/relabel_test.go
index 4c5f4d8d12..d694982ec9 100644
--- a/model/relabel/relabel_test.go
+++ b/model/relabel/relabel_test.go
@@ -874,6 +874,16 @@ separator: ;
 target_label: __meta_kubernetes_pod_container_port_number
 replacement: $1
 action: keepequal
+`,
+		},
+		{
+			name: "Default regex provided",
+			inputYaml: `source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_port]
+separator: ;
+regex: (.*)
+target_label: __meta_kubernetes_pod_container_port_number
+replacement: $1
+action: replace
 `,
 		},
 	}