    fn mul_assign<S: Into<<Self::Scalar as PrimeField>::Repr>>(&mut self, other: S) {
+       if self.is_zero() {
+           return; // 0 *= a equals 0
+       }

+       if other.is_zero() {
+           (*self) = Self::zero(); // a *= 0 equals 0
+           return;
+       }

        let mut res = Self::zero();

        ...
