1 files changed, 4 insertions, 2 deletions
diff --git a/model/riscv_regs.sail b/model/riscv_regs.sail
index cf46390..a085275 100644
--- a/model/riscv_regs.sail
+++ b/model/riscv_regs.sail
@@ -79,7 +79,8 @@ function rX r = {
       28 => x28,
       29 => x29,
       30 => x30,
-      31 => x31
+      31 => x31,
+      _  => {assert(false, "invalid register number"); zero_reg}
     };
   regval_from_reg(v)
 }
@@ -130,7 +131,8 @@ function wX (r, in_v) = {
     28 => x28 = v,
     29 => x29 = v,
     30 => x30 = v,
-    31 => x31 = v
+    31 => x31 = v,
+    _  => assert(false, "invalid register number")
   };
   if (r != 0) then {
      rvfi_wX(r, in_v);