diff --git a/scripts/mbedtls_dev/bignum_common.py b/scripts/mbedtls_dev/bignum_common.py
index 9db567b..03055f0 100644
--- a/scripts/mbedtls_dev/bignum_common.py
+++ b/scripts/mbedtls_dev/bignum_common.py
@@ -267,6 +267,12 @@
     def arg_n(self) -> str:
         return self.format_arg(self.val_n)
 
+    def format_arg(self, val: str) -> str:
+        if self.input_style == "variable":
+            return val.zfill(len(hex(self.int_n)) - 2)
+        else:
+            return super().format_arg(val)
+
     def arguments(self) -> List[str]:
         return [quote_str(self.arg_n)] + super().arguments()