diff --git a/Cargo.toml b/Cargo.toml
index eed0ad8..4cc5d58 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,7 +16,7 @@ futures = "0.3"
 handy_async = "0.2"
 hmac = "0.10.1"
 num = "0.1"
-sha-1 = "0.9.2"
+sha-1 = "0.9.8"
 trackable = "0.1"
 
 openssl = { version = "0.10", optional = true }
diff --git a/src/rfc3711.rs b/src/rfc3711.rs
index 0008d9d..8871093 100644
--- a/src/rfc3711.rs
+++ b/src/rfc3711.rs
@@ -361,6 +361,7 @@ impl Protocol for Srtcp {
 impl<P: Protocol> Context<P>
 where
     u64: From<P::PacketIndex>,
+    P::PacketIndex: Into<BigUint>,
 {
     pub fn new(master_key: &[u8], master_salt: &[u8]) -> Self {
         Context {