diff --git a/builtin.aqua b/builtin.aqua
index f924fe8..9f73bef 100644
--- a/builtin.aqua
+++ b/builtin.aqua
@@ -130,9 +130,9 @@ service Peer("peer"):
     -- Get Unix timestamp in seconds
     timestamp_sec() -> u64
 
-    -- Blocks for the given number of milliseconds. Meant to be used inside `par` blocks.
-    -- If `message` is passed, it's returned after duration has passed
-    timeout(duration_ms: u64, message: ?string) -> ?string
+    -- Blocks for the given number of milliseconds. Meant to be used within `par` blocks.
+    -- message is returned after duration has passed
+    timeout(duration_ms: u64, message: string) -> string
 
 service Kademlia("kad"):
     -- Instructs node to return the locally-known nodes