diff --git a/pkg/admission/plugin/webhook/admission.go b/pkg/admission/plugin/webhook/admission.go
index 2636c58df..8408e89b9 100644
--- a/pkg/admission/plugin/webhook/admission.go
+++ b/pkg/admission/plugin/webhook/admission.go
@@ -298,5 +298,6 @@ func (a *GenericAdmissionWebhook) hookClient(h *v1alpha1.ExternalAdmissionHook)
 	cfg.TLSClientConfig.ServerName = serverName
 	cfg.TLSClientConfig.CAData = h.ClientConfig.CABundle
 	cfg.ContentConfig.NegotiatedSerializer = a.negotiatedSerializer
+	cfg.ContentConfig.ContentType = runtime.ContentTypeJSON
 	return rest.UnversionedRESTClientFor(cfg)
 }