diff --git a/gateware/dragonBoot/windows/descriptorSet.py b/gateware/dragonBoot/windows/descriptorSet.py
index 59c6f34..79089d8 100644
--- a/gateware/dragonBoot/windows/descriptorSet.py
+++ b/gateware/dragonBoot/windows/descriptorSet.py
@@ -223,7 +223,7 @@ def elaborate(self, platform) -> Module:
 				m.d.comb += [
 					self.tx.valid.eq(1),
 					readPort.addr.eq(descriptorDataBaseAddress + wordInStream),
-					self.tx.payload.eq(readPort.data.word_select(3 - byteInStream, 8)),
+					self.tx.payload.eq(readPort.data.word_select((3 - byteInStream).as_unsigned(), 8)),
 					self.tx.first.eq(onFirstPacket),
 					self.tx.last.eq(onLastPacket),
 				]