diff --git a/lib/cartodb/utils/layergroup-metadata.js b/lib/cartodb/utils/layergroup-metadata.js
index 22f7c8f3..ee2e78c4 100644
--- a/lib/cartodb/utils/layergroup-metadata.js
+++ b/lib/cartodb/utils/layergroup-metadata.js
@@ -1,4 +1,5 @@
 const dateWrapper = require('./date-wrapper');
+const querystring = require('querystring');
 
 module.exports = class LayergroupMetadata {
     constructor (resourceLocator) {
@@ -87,7 +88,7 @@ module.exports = class LayergroupMetadata {
     addTileJsonMetadata (layergroup, user, mapconfig, userApiKey = null) {
         const isVectorOnlyMapConfig = mapconfig.isVectorOnlyMapConfig();
         let hasMapnikLayers = false;
-        const apiKey = userApiKey ? `?api_key=${userApiKey}` : '';
+        const apiKey = userApiKey ? '?' + querystring.stringify({api_key: userApiKey}) : '';
 
         layergroup.metadata.layers.forEach((layerMetadata, index) => {
             const layerId = mapconfig.getLayerId(index);