diff --git a/io/Cargo.toml b/io/Cargo.toml
index d245121da..f59c35e00 100644
--- a/io/Cargo.toml
+++ b/io/Cargo.toml
@@ -23,6 +23,9 @@ internals = { package = "bitcoin-internals", version = "0.4.0" }
 
 hashes = { package = "bitcoin_hashes", version = "0.16.0", default-features = false, optional = true }
 
+[dev-dependencies]
+hashes = { package = "bitcoin_hashes", version = "0.16.0", default-features = false, features = ["hex"] }
+
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]