diff --git a/docs/configuration/configuration.md b/docs/configuration/configuration.md
index 8fc479963b..9c97002ace 100644
--- a/docs/configuration/configuration.md
+++ b/docs/configuration/configuration.md
@@ -589,6 +589,7 @@ address with relabeling.
 
 The following meta labels are available on targets during [relabeling](#relabel_config):
 
+* `__meta_gce_instance_id`: the numeric id of the instance
 * `__meta_gce_instance_name`: the name of the instance
 * `__meta_gce_label_<name>`: each GCE label of the instance
 * `__meta_gce_machine_type`: full or partial URL of the machine type of the instance