diff --git a/engine/constants.go b/engine/constants.go
index c0914f53..283a55ce 100644
--- a/engine/constants.go
+++ b/engine/constants.go
@@ -7,3 +7,10 @@ var ContentTypes = map[string]string{
 	"bmp":  "image/bmp",
 	"gif":  "image/gif",
 }
+
+var MimeTypes = []string{
+	"image/jpeg",
+	"image/png",
+	"image/bmp",
+	"image/gif",
+}
diff --git a/engine/engine.go b/engine/engine.go
index c3658141..058b4938 100644
--- a/engine/engine.go
+++ b/engine/engine.go
@@ -30,13 +30,8 @@ func New(cfg config.Config) *Engine {
 
 	if cfg.Backends == nil {
 		b = append(b, Backend{
-			Backend: &backend.GoImage{},
-			mimetypes: []string{
-				"image/jpeg",
-				"image/png",
-				"image/bmp",
-				"image/gif",
-			},
+			Backend:   &backend.GoImage{},
+			mimetypes: MimeTypes,
 		})
 	} else {
 		if cfg.Backends.Lilliput != nil {