diff --git a/src/libstd/num/bigint.rs b/src/libstd/num/bigint.rs
index 498c86dd8e101..53054afb4d2d8 100644
--- a/src/libstd/num/bigint.rs
+++ b/src/libstd/num/bigint.rs
@@ -144,6 +144,8 @@ impl FromStr for BigUint {
     }
 }
 
+impl Num for BigUint {}
+
 impl Shl<uint, BigUint> for BigUint {
     #[inline(always)]
     fn shl(&self, rhs: &uint) -> BigUint {
@@ -788,6 +790,8 @@ impl FromStr for BigInt {
     }
 }
 
+impl Num for BigInt {}
+
 impl Shl<uint, BigInt> for BigInt {
     #[inline(always)]
     fn shl(&self, rhs: &uint) -> BigInt {