diff --git a/des/sim/verilog/tb_des.tcl b/des/sim/verilog/tb_des.tcl
index 46bbb0e..871b489 100644
--- a/des/sim/verilog/tb_des.tcl
+++ b/des/sim/verilog/tb_des.tcl
@@ -7,4 +7,5 @@ lappend signals "tb_des.key"
 lappend signals "tb_des.datain"
 lappend signals "tb_des.validout"
 lappend signals "tb_des.dataout"
+lappend signals "tb_des.outdex"
 set num_added [ gtkwave::addSignalsFromList $signals ]