diff --git a/src/lss/rtl/taxi_i2c_master.sv b/src/lss/rtl/taxi_i2c_master.sv
index 2933710..f5e7ec0 100644
--- a/src/lss/rtl/taxi_i2c_master.sv
+++ b/src/lss/rtl/taxi_i2c_master.sv
@@ -151,6 +151,13 @@ I/O pin.  This would prevent devices from stretching the clock period.
 
 */
 
+// check configuration
+if (s_axis_cmd.DATA_W < 12)
+    $fatal(0, "Command interface width must be at least 12 bits (instance %m)");
+
+if (s_axis_tx.DATA_W != 8 || m_axis_rx.DATA_W != 8)
+    $fatal(0, "Data interface width must be 8 bits (instance %m)");
+
 localparam [3:0]
     STATE_IDLE = 4'd0,
     STATE_ACTIVE_WRITE = 4'd1,
diff --git a/src/lss/rtl/taxi_i2c_slave.sv b/src/lss/rtl/taxi_i2c_slave.sv
index 7f1b5eb..1eceb4a 100644
--- a/src/lss/rtl/taxi_i2c_slave.sv
+++ b/src/lss/rtl/taxi_i2c_slave.sv
@@ -135,6 +135,10 @@ I/O pin.  This would prevent devices from stretching the clock period.
 
 */
 
+// check configuration
+if (s_axis_tx.DATA_W != 8 || m_axis_rx.DATA_W != 8)
+    $fatal(0, "Data interface width must be 8 bits (instance %m)");
+
 localparam [2:0]
     STATE_IDLE = 3'd0,
     STATE_ADDRESS = 3'd1,