diff --git a/system/biu.v b/system/biu.v
index ceda3c5..7e11619 100644
--- a/system/biu.v
+++ b/system/biu.v
@@ -284,7 +284,7 @@ InstrSize InstrSize({INSTRUCTION[31:24],INSTRUCTION[21:19]},Isize);
 wire [2:0] fifoIsize;
 wire Isit1;
 `ifdef EARLY_VALID_INSTRUCTION
-InstrSize fifoInstrSize({INPUT_FIFO[FIFO_start][7:0],INPUT_FIFO[FIFO_start+1][5:3]},fifoIsize);
+InstrSize fifoInstrSize({INPUT_FIFO[FIFO_start][7:0],INPUT_FIFO[FIFO_start+4'd1][5:3]},fifoIsize);
 Is1 Is1(INPUT_FIFO[FIFO_start][7:0],Isit1);
 `endif