diff --git a/custom/idl/fetch.idl b/custom/idl/fetch.idl
new file mode 100644
index 000000000..7cc22b7ed
--- /dev/null
+++ b/custom/idl/fetch.idl
@@ -0,0 +1,14 @@
+// Remove when https://github.com/whatwg/fetch/pull/1647 is merged
+
+ dictionary DeferredRequestInit : RequestInit {
+   DOMHighResTimeStamp activateAfter;
+ };
+
+ [Exposed=Window]
+ interface FetchLaterResult {
+   readonly attribute boolean activated;
+ };
+
+ partial interface Window {
+   [NewObject] FetchLaterResult fetchLater(RequestInfo input, optional DeferredRequestInit init = {});
+ };