diff --git a/src/core/api.js b/src/core/api.js
index cf5b51a5..8eb4cb40 100644
--- a/src/core/api.js
+++ b/src/core/api.js
@@ -197,8 +197,8 @@ export function runAPI(express, app, gitCommit, gitBranch, __dirname) {
         }
 
         streamInfo.headers = new Map([
-            streamInfo.headers || {},
-            req.headers
+            ...(streamInfo.headers || []),
+            ...Object.entries(req.headers)
         ]);
 
         return stream(res, { type: 'internal', ...streamInfo });