diff --git a/hw/cheshire_soc.sv b/hw/cheshire_soc.sv
index b3b625443..d01ac9bac 100644
--- a/hw/cheshire_soc.sv
+++ b/hw/cheshire_soc.sv
@@ -240,7 +240,10 @@ module cheshire_soc import cheshire_pkg::*; #(
     UniqueIds:          0,
     AxiAddrWidth:       Cfg.AddrWidth,
     AxiDataWidth:       Cfg.AxiDataWidth,
-    NoAddrRules:        AxiOut.num_rules
+    NoAddrRules:        AxiOut.num_rules,
+    // Setting a `default` here allows for custom XBars with extended configs outside Cheshire.
+    // Importantly, this requires that '0 *disables* any and all such custom extensions.
+    default: '0
   };
 
   axi_xbar #(