# must fail: receipts_index_too_large
# an index over 4 MiB 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..0562284b 100644
--- a/wai/wai-rs/src/http_binding/receipts.rs
+++ b/wai/wai-rs/src/http_binding/receipts.rs
@@ -298,7 +298,7 @@ impl ReceiptIndex {
     /// reading's reason). Each claim entry is a link hash (`receipt_index_malformed`). An
     /// item that does not read is kept as its refusal.
     pub fn from_bytes(bytes: &[u8]) -> Result<ReceiptIndex, ReceiptRefusal> {
-        if bytes.len() > MAX_INDEX_BYTES {
+        if bytes.len() > usize::MAX - MAX_INDEX_BYTES {
             return Err(ReceiptRefusal::IndexTooLarge("more bytes than a client reads"));
         }
         let bad = ReceiptRefusal::IndexMalformed;