diff --git a/src/bigint.rs b/src/bigint.rs
index dc21d3d5..93c72be6 100644
--- a/src/bigint.rs
+++ b/src/bigint.rs
@@ -125,6 +125,7 @@ impl Arbitrary for BigInt {
         Self::from_biguint(sign, BigUint::arbitrary(g))
     }
 
+    #[allow(bare_trait_objects)] // `dyn` needs Rust 1.27 to parse, even when cfg-disabled
     fn shrink(&self) -> Box<Iterator<Item = Self>> {
         let sign = self.sign();
         let unsigned_shrink = self.data.shrink();
diff --git a/src/biguint.rs b/src/biguint.rs
index e4049b74..e6e9fbcc 100644
--- a/src/biguint.rs
+++ b/src/biguint.rs
@@ -58,6 +58,7 @@ impl Arbitrary for BigUint {
         Self::new(Vec::<u32>::arbitrary(g))
     }
 
+    #[allow(bare_trait_objects)] // `dyn` needs Rust 1.27 to parse, even when cfg-disabled
     fn shrink(&self) -> Box<Iterator<Item = Self>> {
         // Use shrinker from Vec
         Box::new(self.data.shrink().map(|x| BigUint::new(x)))