diff --git a/Cargo.toml b/Cargo.toml
index 22eabe0..0004f8d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,9 +35,9 @@ default-features = false
 version = "1.0"
 
 [features]
-default = ["std", "dep:serde"]
+default = ["std"]
 std = ["chrono/std", "chrono/clock", "alloc"]
-serde = ["chrono/serde"]
+serde = ["dep:serde", "chrono/serde"]
 alloc = ["postcard/alloc", "chrono/alloc"]
 
 [package.metadata.docs.rs]
diff --git a/README.md b/README.md
index ed4e7e4..1545bf0 100644
--- a/README.md
+++ b/README.md
@@ -28,12 +28,15 @@ It also offers optional support for [`serde`](https://serde.rs/). This allows se
 deserializing them with an appropriate `serde` provider like
 [`postcard`](https://github.com/jamesmunns/postcard).
 
-Default features:
+## Default features
 
  - [`std`](https://doc.rust-lang.org/std/): Enables functionality relying on the standard library.
  - [`alloc`](https://doc.rust-lang.org/alloc/): Enables features which operate on containers
    like [`alloc::vec::Vec`](https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html).
    Enabled by the `std` feature.
+
+## Optional Features
+
  - [`serde`](https://serde.rs/): Adds `serde` support for most types by adding `Serialize` and `Deserialize` `derive`s
 
 # Examples
diff --git a/src/ecss.rs b/src/ecss.rs
index 93009ce..f2ccf72 100644
--- a/src/ecss.rs
+++ b/src/ecss.rs
@@ -15,6 +15,16 @@ pub type CrcType = u16;
 pub const CRC_CCITT_FALSE: Crc<u16> = Crc::<u16>::new(&CRC_16_IBM_3740);
 pub const CCSDS_HEADER_LEN: usize = size_of::<crate::zc::SpHeader>();
 
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub enum PusServiceId {
+    Verification = 1,
+    Housekeeping = 3,
+    Event = 5,
+    Action = 8,
+    Test = 17,
+}
+
 /// All PUS versions. Only PUS C is supported by this library.
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
diff --git a/src/lib.rs b/src/lib.rs
index 6faec44..e26d481 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -22,12 +22,15 @@
 //! deserializing them with an appropriate `serde` provider like
 //! [`postcard`](https://github.com/jamesmunns/postcard).
 //!
-//! Default features:
+//! ### Default features
 //!
 //!  - [`std`](https://doc.rust-lang.org/std/): Enables functionality relying on the standard library.
 //!  - [`alloc`](https://doc.rust-lang.org/alloc/): Enables features which operate on containers
 //!     like [`alloc::vec::Vec`](https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html).
 //!     Enabled by the `std` feature.
+//!
+//! ### Optional features
+//!
 //!  - [`serde`](https://serde.rs/): Adds `serde` support for most types by adding `Serialize` and
 //!    `Deserialize` `derive`s
 //!