diff --git a/staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go b/staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go
index ec9870a035a..d94627834da 100644
--- a/staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go
+++ b/staging/src/k8s.io/apiserver/pkg/registry/generic/registry/store.go
@@ -360,6 +360,9 @@ func (e *Store) ListPredicate(ctx context.Context, p storage.SelectionPredicate,
 func finishNothing(context.Context, bool) {}
 
 // Create inserts a new item according to the unique key from the object.
+// Note that registries may mutate the input object (e.g. in the strategy
+// hooks).  Tests which call this might want to call DeepCopy if they expect to
+// be able to examine the input and output objects for differences.
 func (e *Store) Create(ctx context.Context, obj runtime.Object, createValidation rest.ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error) {
 	var finishCreate FinishFunc = finishNothing