diff --git a/lib/spi/src/spi_master.vhd b/lib/spi/src/spi_master.vhd
index 5574b97..c60754c 100644
--- a/lib/spi/src/spi_master.vhd
+++ b/lib/spi/src/spi_master.vhd
@@ -57,8 +57,8 @@ ARCHITECTURE behavior OF spi_master IS
 	signal spi_rst_count			: unsigned(5 downto 0);
 	signal spi_rst					: std_logic;
 
-	signal cat_fifo_din				: unsigned(to_unsigned(cmd)'length-1 downto 0);
-	signal cat_fifo_dout			: unsigned(to_unsigned(cmd)'length-1 downto 0);
+	signal cat_fifo_din				: unsigned(SIZEOF_CMD-1 downto 0);
+	signal cat_fifo_dout			: unsigned(SIZEOF_CMD-1 downto 0);
 	signal cat_fifo_full			: std_logic;
 	signal cat_fifo_empty			: std_logic;
 
@@ -113,7 +113,7 @@ begin
 	GENERIC MAP
 	(
 		addr_width	=> NextExpBaseTwo(CAT_FIFO_DEPTH),
-		data_width	=> cmd_size
+		data_width	=> SIZEOF_CMD
 	)
 	PORT MAP
 	(
diff --git a/lib/spi/src/spi_types.vhd b/lib/spi/src/spi_types.vhd
index 8b1c902..976919d 100644
--- a/lib/spi/src/spi_types.vhd
+++ b/lib/spi/src/spi_types.vhd
@@ -8,6 +8,7 @@ package spi_types is
 	
 	-- Constants
 	constant XFER_MAX_SIZE_BITS	: natural := 32;
+	constant SIZEOF_CMD			: natural := 2*XFER_MAX_SIZE_BITS;
 	
 	-- Types
 	type cmd_t is record
@@ -33,7 +34,6 @@ package spi_types is
 	end record;	
 
 	-- Functions
-	function cmd_size return positive;
 	function to_cmd (xfer_size, data_size : natural) return cmd_t;
 	function to_unsigned (cmd : cmd_t) return unsigned;
 	function to_cmd (cmd : unsigned) return cmd_t;
@@ -42,12 +42,6 @@ end spi_types;
 
 package body spi_types is
 
-	function cmd_size return positive is
-	variable res : cmd_t;
-	begin
-		return res.xfer_size'length + res.data_size'length + 1 + 1;
-	end cmd_size;
-	
 	function to_cmd(xfer_size, data_size : natural) return cmd_t is
 	variable res : cmd_t;
 	begin
@@ -57,7 +51,7 @@ package body spi_types is
 	end to_cmd;	
 	
 	function to_unsigned(cmd : cmd_t) return unsigned is
-	variable res : unsigned(cmd.xfer_size'length + cmd.data_size'length + 1 + 1 -1 downto 0) := (others => '0');
+	variable res : unsigned(SIZEOF_CMD-1 downto 0) := (others => '0');
 	begin
 		res(res'left downto res'left - cmd.xfer_size'length+1) := cmd.xfer_size;
 		res(res'left - cmd.xfer_size'length downto res'left - cmd.xfer_size'length - cmd.data_size'length +1) := cmd.data_size;
@@ -68,7 +62,7 @@ package body spi_types is
 	variable res : cmd_t;
 	begin
 		res.xfer_size := cmd(cmd'left downto cmd'left - res.xfer_size'length+1);
-		res.data_size := cmd(cmd'left - res.xfer_size'length downto cmd'left - res.xfer_size'length - res.data_size'length +1);
+		res.data_size := cmd(cmd'left - res.xfer_size'length downto 0);
 		
 		return res;
 	end to_cmd;