diff --git a/hashes/Cargo.toml b/hashes/Cargo.toml
index 54bd229a7..4d048ea84 100644
--- a/hashes/Cargo.toml
+++ b/hashes/Cargo.toml
@@ -15,7 +15,7 @@ exclude = ["tests", "contrib"]
 
 [features]
 default = ["std"]
-std = ["alloc", "hex/std", "bitcoin-io/std"]
+std = ["alloc", "hex/std", "bitcoin-io?/std"]
 alloc = ["hex/alloc"]
 schemars = ["dep:schemars", "alloc"]
 # If you want I/O you must enable either "std" or "io".