diff --git a/hugolib/site.go b/hugolib/site.go
index ee4add770..15e78d223 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -64,7 +64,7 @@ type Site struct {
 	Info        SiteInfo
 	Shortcodes  map[string]ShortcodeFunc
 	timer       *nitro.B
-	Transformer *transform.Transformer
+	Transformer transform.Transformer
 	Target      target.Output
 	Alias       target.AliasPublisher
 }
@@ -618,7 +618,7 @@ func (s *Site) WritePublic(path string, content io.Reader) (err error) {
 	}
 
 	if s.Transformer == nil {
-		s.Transformer = &transform.Transformer{BaseURL: s.Config.BaseUrl}
+		s.Transformer = &transform.AbsURL{BaseURL: s.Config.BaseUrl}
 	}
 	final := new(bytes.Buffer)
 	s.Transformer.Apply(content, final)
diff --git a/transform/post.go b/transform/post.go
index be383700d..c89a7bdf2 100644
--- a/transform/post.go
+++ b/transform/post.go
@@ -6,11 +6,15 @@ import (
 	"net/url"
 )
 
-type Transformer struct {
+type Transformer interface {
+	Apply(io.Reader, io.Writer) error
+}
+
+type AbsURL struct {
 	BaseURL string
 }
 
-func (t *Transformer) Apply(r io.Reader, w io.Writer) (err error) {
+func (t *AbsURL) Apply(r io.Reader, w io.Writer) (err error) {
 	var tr *htmltran.Transformer
 
 	if tr, err = htmltran.NewFromReader(r); err != nil {
@@ -28,7 +32,7 @@ type elattr struct {
 	tag, attr string
 }
 
-func (t *Transformer) absUrlify(tr *htmltran.Transformer, selectors ...elattr) (err error) {
+func (t *AbsURL) absUrlify(tr *htmltran.Transformer, selectors ...elattr) (err error) {
 	var baseURL, inURL *url.URL
 
 	if baseURL, err = url.Parse(t.BaseURL); err != nil {
diff --git a/transform/posttrans_test.go b/transform/posttrans_test.go
index 08fe18c11..d35847af3 100644
--- a/transform/posttrans_test.go
+++ b/transform/posttrans_test.go
@@ -26,7 +26,7 @@ func TestAbsUrlify(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		tr := &Transformer{
+		tr := &AbsURL{
 			BaseURL: "http://base",
 		}
 		out := new(bytes.Buffer)