diff --git a/model/riscv_sys_regs.sail b/model/riscv_sys_regs.sail
index ecc7735b7..dad4a9de9 100644
--- a/model/riscv_sys_regs.sail
+++ b/model/riscv_sys_regs.sail
@@ -213,6 +213,9 @@ function haveZmmul()  -> bool = true
 /* Zicond extension support */
 function haveZicond() -> bool = true
 
+/* Zacas extension support. */
+function haveZacas()  -> bool = true
+
 bitfield Mstatush : bits(32) = {
   MBE  : 5,
   SBE  : 4