diff --git a/client/src/templates/Challenges/utils/build.js b/client/src/templates/Challenges/utils/build.js
index 62507a5f94..c07a0f5001 100644
--- a/client/src/templates/Challenges/utils/build.js
+++ b/client/src/templates/Challenges/utils/build.js
@@ -48,10 +48,19 @@ const composeFunctions = (...fns) =>
   fns.map(applyFunction).reduce((f, g) => x => f(x).then(g));
 
 function buildSourceMap(files) {
-  return files.reduce((sources, file) => {
-    sources[file.name] = file.source || file.contents;
-    return sources;
-  }, {});
+  // TODO: concatenating the source/contents is a quick hack for multi-file
+  // editing. It is used because all the files (js, html and css) end up with
+  // the same name 'index'. This made the last file the only file to  appear in
+  // sources.
+  // A better solution is to store and handle them separately. Perhaps never
+  // setting the name to 'index'.
+  return files.reduce(
+    (sources, file) => {
+      sources[file.name] += file.source || file.contents;
+      return sources;
+    },
+    { index: '' }
+  );
 }
 
 function checkFilesErrors(files) {