diff --git a/routes/dynamic-enum.js b/routes/dynamic-enum.js
index 7eb5b2dd..05cf8042 100644
--- a/routes/dynamic-enum.js
+++ b/routes/dynamic-enum.js
@@ -19,7 +19,8 @@ function getHighlightEnumTitles(item) {
 
 function getPrognosisStartEnum(item) {
   try {
-    return [null].concat(Object.keys(getFirstColumnSerie(item.data).map(key => parseInt(key))));
+    // constructs an array like [null,0,1,2,3,...] with the indexes from the first data column
+    return [null].concat([...getFirstColumnSerie(item.data).keys()]);
   } catch (e) {
     return [null]
   }
@@ -58,4 +59,4 @@ module.exports = {
 
     return reply(Boom.badRequest());
   }
-}
\ No newline at end of file
+}