diff -r fe7fc19b1e64 sys/src/cmd/rio/xfid.c
--- a/sys/src/cmd/rio/xfid.c	Sun Nov 03 15:20:57 2019 +0100
+++ b/sys/src/cmd/rio/xfid.c	Tue Nov 19 11:42:16 2019 +1030
@@ -670,9 +670,9 @@
 		}
 		c1 = crm.c1;
 		c2 = crm.c2;
-		t = emalloc(cnt+UTFmax+1);	/* room to unpack partial rune plus */
+		pair.ns = cnt+UTFmax+1;	/* room for partial rune and null byte */
+		t = emalloc(pair.ns);
 		pair.s = t;
-		pair.ns = cnt;
 		send(c1, &pair);
 		recv(c2, &pair);
 		fc.data = pair.s;