add default nettype none
diff --git a/verilog/rtl/gpio_control_block.v b/verilog/rtl/gpio_control_block.v
index bca5aa3..ed3d531 100644
--- a/verilog/rtl/gpio_control_block.v
+++ b/verilog/rtl/gpio_control_block.v
@@ -1,3 +1,4 @@
+`default_nettype none
 /* 
  *---------------------------------------------------------------------
  * See gpio_control_block for description.  This module is like