diff --git a/lib/sbi_ecall.c b/lib/sbi_ecall.c
index 6312469d..94c6e770 100644
--- a/lib/sbi_ecall.c
+++ b/lib/sbi_ecall.c
@@ -86,6 +86,8 @@ int sbi_ecall_handler(u32 hartid, ulong mcause,
 		ret = 0;
 		break;
 	default:
+		regs->a0 = SBI_ENOTSUPP;
+		ret = 0;
 		break;
 	};