diff --git a/crates/optimism/primitives/Cargo.toml b/crates/optimism/primitives/Cargo.toml
index 9a11f0f38e11..d75f35614840 100644
--- a/crates/optimism/primitives/Cargo.toml
+++ b/crates/optimism/primitives/Cargo.toml
@@ -35,6 +35,9 @@ zstd = { workspace = true, optional = true }
 serde.workspace = true
 arbitrary = { workspace = true, features = ["derive"], optional = true }
 
+# io
+serde.workspace = true
+
 # misc
 derive_more = { workspace = true, features = ["deref", "from", "constructor"] }
 proptest = { workspace = true, optional = true }
diff --git a/crates/primitives-traits/src/signature.rs b/crates/primitives-traits/src/signature.rs
index 85047fbcee70..61d5dcf907c4 100644
--- a/crates/primitives-traits/src/signature.rs
+++ b/crates/primitives-traits/src/signature.rs
@@ -58,8 +58,6 @@ pub trait Signature: Sized + Send + Sync {
     fn extract_chain_id(v: u64) -> alloy_rlp::Result<(bool, Option<u64>)>;
 }
 
-// todo: add optimism type that wraps Signature, to impl separately for OP to account for system
-// null signature
 impl Signature for alloy_primitives::Signature {
     fn r(&self) -> U256 {
         Self::r(self)