diff --git a/scripts/mbedtls_dev/ecp.py b/scripts/mbedtls_dev/ecp.py
index b7b66e418..5d0de2654 100644
--- a/scripts/mbedtls_dev/ecp.py
+++ b/scripts/mbedtls_dev/ecp.py
@@ -672,8 +672,7 @@ class EcpP256K1Raw(bignum_common.ModOperationCommon,
 
     @property
     def arg_a(self) -> str:
-        hex_digits = bignum_common.hex_digits_for_limb(448 // self.bits_in_limb, self.bits_in_limb)
-        return super().format_arg('{:x}'.format(self.int_a)).zfill(hex_digits)
+        return super().format_arg('{:x}'.format(self.int_a)).zfill(2 * self.hex_digits)
 
     def result(self) -> List[str]:
         result = self.int_a % self.int_n