diff --git a/x-pack/plugins/rollup/server/routes/api/index_patterns.js b/x-pack/plugins/rollup/server/routes/api/index_patterns.js
index 7f760ac515896e..04c313f9b3ba16 100644
--- a/x-pack/plugins/rollup/server/routes/api/index_patterns.js
+++ b/x-pack/plugins/rollup/server/routes/api/index_patterns.js
@@ -69,7 +69,7 @@ export function registerFieldsForWildcardRoute(server) {
         const mergedRollupFields = mergeCapabilitiesWithFields(rollupIndexCapabilities, fieldsFromFieldCapsApi, rollupFields);
 
         return {
-          fields: [ ...rollupFields, ...mergedRollupFields ]
+          fields: mergedRollupFields
         };
       } catch(err) {
         if (isEsError(err)) {