diff --git a/src/eth/rtl/us/taxi_eth_mac_25g_us_ch.sv b/src/eth/rtl/us/taxi_eth_mac_25g_us_ch.sv
index 5b40e24..9a5ab51 100644
--- a/src/eth/rtl/us/taxi_eth_mac_25g_us_ch.sv
+++ b/src/eth/rtl/us/taxi_eth_mac_25g_us_ch.sv
@@ -1139,6 +1139,9 @@ end else begin : mac
 
     localparam CTRL_W = DATA_W / 8;
 
+    if (USXGMII_EN)
+        $fatal(0, "Error: USXGMII is not currently supported in split MAC/PHY configuration (instance %m)");
+
     wire [DATA_W-1:0]  xgmii_txd;
     wire [CTRL_W-1:0]  xgmii_txc;
     wire               xgmii_tx_valid;