diff --git a/pkg/apis/core/types.go b/pkg/apis/core/types.go
index 43146537870..9a74daecce3 100644
--- a/pkg/apis/core/types.go
+++ b/pkg/apis/core/types.go
@@ -4206,6 +4206,7 @@ type PodSignature struct {
 // ContainerImage describe a container image
 type ContainerImage struct {
 	// Names by which this image is known.
+	// +optional
 	Names []string
 	// The size of the image in bytes.
 	// +optional
diff --git a/staging/src/k8s.io/api/core/v1/types.go b/staging/src/k8s.io/api/core/v1/types.go
index 6d98efa56bd..d5e86a7c7b8 100644
--- a/staging/src/k8s.io/api/core/v1/types.go
+++ b/staging/src/k8s.io/api/core/v1/types.go
@@ -4872,6 +4872,7 @@ type PodSignature struct {
 type ContainerImage struct {
 	// Names by which this image is known.
 	// e.g. ["k8s.gcr.io/hyperkube:v1.0.7", "dockerhub.io/google_containers/hyperkube:v1.0.7"]
+	// +optional
 	Names []string `json:"names" protobuf:"bytes,1,rep,name=names"`
 	// The size of the image in bytes.
 	// +optional