diff --git a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go
index 8daa1f960ff..9c2798f0307 100644
--- a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go
+++ b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go
@@ -85,7 +85,8 @@ type CustomResourceDefinitionSpec struct {
 type CustomResourceConversion struct {
 	// `strategy` specifies the conversion strategy. Allowed values are:
 	// - `None`: The converter only change the apiVersion and would not touch any other field in the CR.
-	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.
+	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information
+	//   is needed for this option. This requires spec.preserveUnknownFields to be false.
 	Strategy ConversionStrategyType
 
 	// `webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`.
diff --git a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go
index 63e25245d82..6d931ca95c1 100644
--- a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go
+++ b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go
@@ -90,7 +90,8 @@ type CustomResourceDefinitionSpec struct {
 type CustomResourceConversion struct {
 	// `strategy` specifies the conversion strategy. Allowed values are:
 	// - `None`: The converter only change the apiVersion and would not touch any other field in the CR.
-	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information is needed for this option.
+	// - `Webhook`: API Server will call to an external webhook to do the conversion. Additional information
+	//   is needed for this option. This requires spec.preserveUnknownFields to be false.
 	Strategy ConversionStrategyType `json:"strategy" protobuf:"bytes,1,name=strategy"`
 
 	// `webhookClientConfig` is the instructions for how to call the webhook if strategy is `Webhook`. This field is