diff --git a/Cargo.toml b/Cargo.toml
index fe90e8e3..4374ce0d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -34,3 +34,5 @@ serde_derive = "<1.0.99"
 serde_json = "<1.0.45"
 serde_test = "1"
 secp256k1 = { version = "0.17.1", features = ["rand-std"] }
+# We need to pin ryu (transitive dep from serde_json) to stay compatible with Rust 1.22.0
+ryu = "<1.0.5"