diff --git a/modules/alu.sv b/modules/alu.sv
index 0fe5f4b..7fb1069 100644
--- a/modules/alu.sv
+++ b/modules/alu.sv
@@ -6,6 +6,7 @@
 
 // flags[0:0] = Cout
 // flags[1:1] = Overflow
+// flags[2:2] = Zero
 module alu #(parameter width=2)(input logic [3:0] op,
     input logic [2**width-1:0] A, input logic [2**width-1:0] B,
     output logic [2**width-1:0] OUT_1, output logic[2:0] flags