diff --git a/cmd/adapter/adapter.go b/cmd/adapter/adapter.go
index 8dfa97cb..8a9f7acb 100644
--- a/cmd/adapter/adapter.go
+++ b/cmd/adapter/adapter.go
@@ -28,6 +28,7 @@ import (
 	"strings"
 	"time"
 
+	customexternalmetrics "github.com/kubernetes-sigs/custom-metrics-apiserver/pkg/apiserver"
 	basecmd "github.com/kubernetes-sigs/custom-metrics-apiserver/pkg/cmd"
 	"github.com/kubernetes-sigs/custom-metrics-apiserver/pkg/provider"
 
@@ -278,7 +279,7 @@ func main() {
 	}
 	cmd.Name = "prometheus-metrics-adapter"
 
-	cmd.OpenAPIConfig = genericapiserver.DefaultOpenAPIConfig(generatedopenapi.GetOpenAPIDefinitions, openapinamer.NewDefinitionNamer(api.Scheme))
+	cmd.OpenAPIConfig = genericapiserver.DefaultOpenAPIConfig(generatedopenapi.GetOpenAPIDefinitions, openapinamer.NewDefinitionNamer(api.Scheme, customexternalmetrics.Scheme))
 	cmd.OpenAPIConfig.Info.Title = "prometheus-metrics-adapter"
 	cmd.OpenAPIConfig.Info.Version = "1.0.0"