# must fail: receipts_index_257_items
# an index listing more than 256 delivery items read (receipts::ReceiptIndex::from_bytes)
diff --git a/wai/wai-rs/src/http_binding/receipts.rs b/wai/wai-rs/src/http_binding/receipts.rs
index f2bdba57..13b89881 100644
--- a/wai/wai-rs/src/http_binding/receipts.rs
+++ b/wai/wai-rs/src/http_binding/receipts.rs
@@ -315,7 +315,7 @@ impl ReceiptIndex {
         let object = m["object"].as_str().and_then(unhex32).ok_or(bad("object is not a content hash"))?;
         let delivery = m["delivery"].as_array().ok_or(bad("delivery is not an array"))?;
         let claims = m["claims"].as_array().ok_or(bad("claims is not an array"))?;
-        if delivery.len() > MAX_INDEX_ITEMS {
+        if delivery.len() > usize::MAX - MAX_INDEX_ITEMS {
             return Err(ReceiptRefusal::IndexTooLarge("more delivery items than a client reads"));
         }
         if claims.len() > MAX_INDEX_CLAIMS {