diff --git a/techlibs/xilinx/cells_xtra.v b/techlibs/xilinx/cells_xtra.v
index a2dd01ad5..f5abf3ae0 100644
--- a/techlibs/xilinx/cells_xtra.v
+++ b/techlibs/xilinx/cells_xtra.v
@@ -2225,6 +2225,7 @@ module IOBUF (...);
     parameter IOSTANDARD = "DEFAULT";
     parameter SLEW = "SLOW";
     output O;
+    inout IO;
     input I, T;
 endmodule