diff --git a/librustzcash/src/rustzcash.rs b/librustzcash/src/rustzcash.rs
index 1db70ac..4f27fa1 100644
--- a/librustzcash/src/rustzcash.rs
+++ b/librustzcash/src/rustzcash.rs
@@ -1002,8 +1002,11 @@ pub extern "system" fn librustzcash_sapling_spend_sig(
         Err(_) => return false,
     };
 
+    // Initialize secure RNG
+    let mut rng = OsRng;
+
     // Do the signing
-    let sig = spend_sig(ask, ar, unsafe { &*sighash }, &JUBJUB);
+    let sig = spend_sig(ask, ar, unsafe { &*sighash }, &mut rng, &JUBJUB);
 
     // Write out the signature
     sig.write(&mut (unsafe { &mut *result })[..])
diff --git a/zcash_primitives/src/sapling.rs b/zcash_primitives/src/sapling.rs
index ad7e309..bd981e6 100644
--- a/zcash_primitives/src/sapling.rs
+++ b/zcash_primitives/src/sapling.rs
@@ -2,7 +2,7 @@
 
 use ff::{BitIterator, PrimeField, PrimeFieldRepr};
 use pairing::bls12_381::{Bls12, Fr, FrRepr};
-use rand_os::OsRng;
+use rand_core::{CryptoRng, RngCore};
 use sapling_crypto::{
     jubjub::{fs::Fs, FixedGenerators, JubjubBls12},
     pedersen_hash::{pedersen_hash, Personalization},
@@ -106,15 +106,13 @@ lazy_static! {
 }
 
 /// Create the spendAuthSig for a Sapling SpendDescription.
-pub fn spend_sig(
+pub fn spend_sig<R: RngCore + CryptoRng>(
     ask: PrivateKey<Bls12>,
     ar: Fs,
     sighash: &[u8; 32],
+    rng: &mut R,
     params: &JubjubBls12,
 ) -> Signature {
-    // Initialize secure RNG
-    let mut rng = OsRng;
-
     // We compute `rsk`...
     let rsk = ask.randomize(ar);
 
@@ -130,7 +128,7 @@ pub fn spend_sig(
     // Do the signing
     rsk.sign(
         &data_to_be_signed,
-        &mut rng,
+        rng,
         FixedGenerators::SpendingKeyGenerator,
         params,
     )
diff --git a/zcash_primitives/src/transaction/builder.rs b/zcash_primitives/src/transaction/builder.rs
index 4edcd20..5c0e643 100644
--- a/zcash_primitives/src/transaction/builder.rs
+++ b/zcash_primitives/src/transaction/builder.rs
@@ -522,6 +522,7 @@ impl<R: RngCore + CryptoRng> Builder<R> {
                 PrivateKey(spend.extsk.expsk.ask),
                 spend.alpha,
                 &sighash,
+                &mut self.rng,
                 &JUBJUB,
             ));
         }