diff --git a/rtl/serv_decode.v b/rtl/serv_decode.v
index 7b9a9fd..de6deed 100644
--- a/rtl/serv_decode.v
+++ b/rtl/serv_decode.v
@@ -73,13 +73,12 @@ module serv_decode
    reg       imm25;
    reg       imm30;
 
-   wire op_or_opimm = (!opcode[4] & opcode[2] & !opcode[0]);
    wire co_mdu_op     = MDU & (opcode == 5'b01100) & imm25;
 
    wire co_two_stage_op =
 	~opcode[2] | (funct3[0] & ~funct3[1] & ~opcode[0] & ~opcode[4]) |
 	(funct3[1] & ~funct3[2] & ~opcode[0] & ~opcode[4]) | co_mdu_op;
-   wire co_shift_op   = op_or_opimm & (funct3[1:0] == 2'b01) & !co_mdu_op;
+   wire co_shift_op = (opcode[2] & ~funct3[1]) & !co_mdu_op;
    wire co_slt_or_branch = (opcode[4] | (funct3[1] & opcode[2]) | (imm30 & opcode[2] & opcode[3] & ~funct3[2])) & !co_mdu_op;
    wire co_branch_op = opcode[4];
    wire co_dbus_en    = ~opcode[2] & ~opcode[4];