diff --git a/sys/src/9/pc/ether8139.c b/sys/src/9/pc/ether8139.c
index f9596ac7d..258869d9e 100644
--- a/sys/src/9/pc/ether8139.c
+++ b/sys/src/9/pc/ether8139.c
@@ -479,7 +479,7 @@ rtl8139txstart(Ether* edev)
 		size = BLEN(bp);
 
 		td = &ctlr->td[ctlr->tdh];
-		if(((int)bp->rp) & 0x03){
+		if(((uintptr)bp->rp) & 0x03){
 			memmove(td->data, bp->rp, size);
 			freeb(bp);
 			csr32w(ctlr, td->tsad, PCIWADDR(td->data));