@@ -243,6 +243,7 @@ impl Num for BigUint {
b'0'...b'9' => b - b'0',
b'a'...b'z' => b - b'a' + 10,
b'A'...b'Z' => b - b'A' + 10,
+ b'_' => continue,
_ => u8::MAX,
};
if d < radix as u8 {