diff --git a/ff/ff_derive/Cargo.toml b/ff/ff_derive/Cargo.toml
index 4adf28b31..89a45b315 100644
--- a/ff/ff_derive/Cargo.toml
+++ b/ff/ff_derive/Cargo.toml
@@ -16,8 +16,8 @@ edition = "2018"
 proc-macro = true
 
 [dependencies]
-addchain = "0.1"
-num-bigint = "0.2"
+addchain = "0.2"
+num-bigint = "0.3"
 num-traits = "0.2"
 num-integer = "0.1"
 proc-macro2 = "1"
diff --git a/ff/ff_derive/src/lib.rs b/ff/ff_derive/src/lib.rs
index 7e3a4abac..c5c811ab3 100644
--- a/ff/ff_derive/src/lib.rs
+++ b/ff/ff_derive/src/lib.rs
@@ -419,7 +419,8 @@ fn biguint_to_real_u64_vec(mut v: BigUint, limbs: usize) -> Vec<u64> {
     let mut ret = vec![];
 
     while v > BigUint::zero() {
-        ret.push((&v % &m).to_u64().unwrap());
+        let limb: BigUint = &v % &m;
+        ret.push(limb.to_u64().unwrap());
         v >>= 64;
     }