diff --git a/lib/cartodb/controllers/named_maps.js b/lib/cartodb/controllers/named_maps.js
index 6936332f..8dbc27d1 100644
--- a/lib/cartodb/controllers/named_maps.js
+++ b/lib/cartodb/controllers/named_maps.js
@@ -27,7 +27,7 @@ NamedMapsController.prototype.register = function(app) {
 
 NamedMapsController.prototype.sendResponse = function(req, res, resource, headers, namedMapProvider) {
     this.surrogateKeysCache.tag(res, new NamedMapsCacheEntry(req.context.user, namedMapProvider.getTemplateName()));
-    res.header('Content-Type', headers['Content-Type']);
+    res.header('Content-Type', headers['content-type'] || headers['Content-Type'] || 'image/png');
     res.header('Cache-Control', 'public,max-age=7200,must-revalidate');
 
     var self = this;