diff --git a/detectors/gcp/cloud-run.go b/detectors/gcp/cloud-run.go
index 78757dae195..685c5c54355 100644
--- a/detectors/gcp/cloud-run.go
+++ b/detectors/gcp/cloud-run.go
@@ -28,6 +28,8 @@ import (
 
 const serviceNamespace = "cloud-run-managed"
 
+// The minimal list of metadata.Client methods we use. Use an interface so we
+// can replace it with a fake implementation in the unit test.
 type metadataClient interface {
 	ProjectID() (string, error)
 	Get(string) (string, error)