diff --git a/src/browser/webapi/net/Fetch.zig b/src/browser/webapi/net/Fetch.zig
index ca565056e..8a7fbd6e3 100644
--- a/src/browser/webapi/net/Fetch.zig
+++ b/src/browser/webapi/net/Fetch.zig
@@ -94,7 +94,7 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
 
         try authored.ensureUnusedCapacity(exec.call_arena, h._list._entries.items.len);
         for (h._list._entries.items) |entry| {
-            authored.appendAssumeCapacity(entry.name.str());
+            authored.appendAssumeCapacity(try exec.call_arena.dupe(u8, entry.name.str()));
         }
     }
     try exec.headersForRequest(&headers);
diff --git a/src/browser/webapi/net/XMLHttpRequest.zig b/src/browser/webapi/net/XMLHttpRequest.zig
index d280b8694..f3a4d3ceb 100644
--- a/src/browser/webapi/net/XMLHttpRequest.zig
+++ b/src/browser/webapi/net/XMLHttpRequest.zig
@@ -266,7 +266,7 @@ pub fn send(self: *XMLHttpRequest, body_: ?BodyInit, exec_: *const Execution) !v
     const req_headers = self._request_headers._list._entries.items;
     var authored: std.ArrayList([]const u8) = try .initCapacity(exec.call_arena, req_headers.len);
     for (req_headers) |entry| {
-        authored.appendAssumeCapacity(entry.name.str());
+        authored.appendAssumeCapacity(try exec.call_arena.dupe(u8, entry.name.str()));
     }
 
     if (cookie_support) {