diff --git a/Cargo.toml b/Cargo.toml
index 3f187ce2..dd1dc405 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [workspace]
-members = ["derive", ".", "codetable"]
+members = ["derive", "derive-impl", ".", "codetable"]
 
 [package]
 name = "multihash"
@@ -38,3 +38,4 @@ hex = "0.4.2"
 serde_json = "1.0.58"
 quickcheck = "1.0.3"
 arbitrary = "1.1.0"
+rand = { version = "0.8.5", features = ["small_rng"] }
diff --git a/codetable/Cargo.toml b/codetable/Cargo.toml
index 86107080..25e53018 100644
--- a/codetable/Cargo.toml
+++ b/codetable/Cargo.toml
@@ -16,7 +16,6 @@ sha-3 = { version = "0.10.0", default-features = false, package = "sha3" }
 strobe-rs = { version = "0.7.0", default-features = false }
 ripemd-rs = { package = "ripemd", version = "0.1.1"}
 multihash-derive = { version = "0.8.0", path = "../derive", default-features = false }
-multihash = { version = "0.18.0", path = "../" }
 
 [dev-dependencies]
 hex = "0.4.2"
diff --git a/codetable/benches/multihash.rs b/codetable/benches/multihash.rs
index ee160d6c..5d964a66 100644
--- a/codetable/benches/multihash.rs
+++ b/codetable/benches/multihash.rs
@@ -1,10 +1,10 @@
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
-use multihash::Hasher;
 use multihash_codetable::{
     Blake2b256, Blake2b512, Blake2s128, Blake2s256, Blake3_256, Keccak224, Keccak256, Keccak384,
     Keccak512, Sha1, Sha2_256, Sha2_512, Sha3_224, Sha3_256, Sha3_384, Sha3_512, Strobe256,
     Strobe512,
 };
+use multihash_derive::Hasher;
 use rand::Rng;
 
 macro_rules! group_digest {
diff --git a/codetable/examples/custom_table.rs b/codetable/examples/custom_table.rs
index 99287d17..40235d0d 100644
--- a/codetable/examples/custom_table.rs
+++ b/codetable/examples/custom_table.rs
@@ -1,8 +1,7 @@
 use std::convert::TryFrom;
 
-use multihash::{Hasher, MultihashDigest as _};
 use multihash_codetable::Sha2_256;
-use multihash_derive::MultihashDigest;
+use multihash_derive::{Hasher, MultihashDigest};
 
 // You can implement a custom hasher. This is a SHA2 256-bit hasher that returns a hash that is
 // truncated to 160 bits.
diff --git a/codetable/examples/manual_mh.rs b/codetable/examples/manual_mh.rs
index 11f35f52..c3905591 100644
--- a/codetable/examples/manual_mh.rs
+++ b/codetable/examples/manual_mh.rs
@@ -1,5 +1,5 @@
-use multihash::MultihashDigest;
 use multihash_codetable::Code;
+use multihash_derive::MultihashDigest;
 
 /// prefix/multihash generating tool to aid when adding new tests
 fn prefix_util() {
diff --git a/codetable/src/hasher_impl.rs b/codetable/src/hasher_impl.rs
index 8fd204bd..5c67523a 100644
--- a/codetable/src/hasher_impl.rs
+++ b/codetable/src/hasher_impl.rs
@@ -1,4 +1,4 @@
-use multihash::Hasher;
+use multihash_derive::Hasher;
 
 use std::io;
 
@@ -153,7 +153,7 @@ macro_rules! derive_rustcrypto_hasher {
             }
         }
 
-        impl ::multihash::Hasher for $name {
+        impl ::multihash_derive::Hasher for $name {
             fn update(&mut self, input: &[u8]) {
                 use digest::Digest;
                 self.state.update(input)
diff --git a/codetable/src/lib.rs b/codetable/src/lib.rs
index 24abbcd2..d9329350 100644
--- a/codetable/src/lib.rs
+++ b/codetable/src/lib.rs
@@ -88,8 +88,8 @@ pub enum Code {
 mod tests {
     use super::*;
     use crate::hasher_impl::sha3::{Sha3_256, Sha3_512};
-    use multihash::MultihashDigest;
-    use multihash::{Hasher, Multihash};
+    use multihash_derive::MultihashDigest;
+    use multihash_derive::{Hasher, Multihash};
 
     #[test]
     fn test_hasher_256() {
diff --git a/codetable/tests/lib.rs b/codetable/tests/lib.rs
index 7e388573..8e3f1e5f 100644
--- a/codetable/tests/lib.rs
+++ b/codetable/tests/lib.rs
@@ -1,11 +1,11 @@
 use std::io::{Cursor, Write};
 
-use multihash::{Hasher, MultihashDigest};
 use multihash_codetable::{
     Blake2b256, Blake2b512, Blake2s128, Blake2s256, Blake3_256, Identity256, Keccak224, Keccak256,
     Keccak384, Keccak512, Sha1, Sha2_256, Sha2_512, Sha3_224, Sha3_256, Sha3_384, Sha3_512,
     Strobe256, Strobe512,
 };
+use multihash_derive::{Hasher, MultihashDigest};
 
 #[derive(Clone, Copy, Debug, Eq, multihash_derive::MultihashDigest, PartialEq)]
 #[mh(alloc_size = 64)]
@@ -386,8 +386,8 @@ fn multihash_errors() {
 
 #[test]
 fn blak3_non_default_digest() {
-    use multihash::MultihashDigest;
     use multihash_codetable::Blake3Hasher;
+    use multihash_derive::MultihashDigest;
     const DIGEST_SIZE: usize = 16;
     pub struct ContentHasher(Blake3Hasher<DIGEST_SIZE>);
 
diff --git a/derive-impl/Cargo.toml b/derive-impl/Cargo.toml
new file mode 100644
index 00000000..da935b8b
--- /dev/null
+++ b/derive-impl/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "multihash-derive-impl"
+version = "0.1.0"
+authors = ["David Craven <david@craven.ch>"]
+edition = "2018"
+description = "Proc macro for deriving custom multihash tables."
+license = "MIT"
+repository = "https://github.com/multiformats/multihash"
+resolver = "2"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = { version = "1.0.24", features = ["span-locations"] }
+proc-macro-crate = "~1.1.0"
+proc-macro-error = "1.0.4"
+quote = "1.0.7"
+syn = "1.0.42"
+synstructure = "0.12.4"
+
+[features]
+default = ["std"]
+std = []
+
+[dev-dependencies]
+pretty_assertions = "1.0.0"
+#multihash = { path = "..", default-features = false, features = ["derive", "sha2"] }
diff --git a/derive-impl/src/lib.rs b/derive-impl/src/lib.rs
new file mode 100644
index 00000000..4c990ee3
--- /dev/null
+++ b/derive-impl/src/lib.rs
@@ -0,0 +1,66 @@
+//! This proc macro derives a custom Multihash code table from a list of hashers. It also
+//! generates a public type called `Multihash` which corresponds to the specified `alloc_size`.
+//!
+//! The digests are stack allocated with a fixed size. That size needs to be big enough to hold any
+//! of the specified hash digests. This cannot be determined reliably on compile-time, hence it
+//! needs to set manually via the `alloc_size` attribute. Also you might want to set it to bigger
+//! sizes then necessarily needed for backwards/forward compatibility.
+//!
+//! If you set `#mh(alloc_size = …)` to a too low value, you will get compiler errors. Please note
+//! the the sizes are checked only on a syntactic level and *not* on the type level. This means
+//! that digest need to have a size const generic, which is a valid `usize`, for example `32` or
+//! `64`.
+//!
+//! You can disable those compiler errors with setting the `no_alloc_size_errors` attribute. This
+//! can be useful if you e.g. have specified type aliases for your hash digests and you are sure
+//! you use the correct value for `alloc_size`.
+//!
+//! # Example
+//!
+//! ```
+//! use multihash::derive::Multihash;
+//! use multihash::MultihashDigest;
+//!
+//! #[derive(Clone, Copy, Debug, Eq, Multihash, PartialEq)]
+//! #[mh(alloc_size = 64)]
+//! pub enum Code {
+//!     #[mh(code = 0x01, hasher = multihash::Sha2_256)]
+//!     Foo,
+//!     #[mh(code = 0x02, hasher = multihash::Sha2_512)]
+//!     Bar,
+//! }
+//!
+//! let hash = Code::Foo.digest(b"hello world!");
+//! println!("{:02x?}", hash);
+//! ```
+extern crate proc_macro;
+
+mod multihash;
+mod utils;
+
+use proc_macro::TokenStream;
+use proc_macro_error::proc_macro_error;
+use synstructure::macros::{parse, DeriveInput};
+use synstructure::{MacroResult, Structure};
+
+#[proc_macro_derive(Multihash, attributes(mh))]
+#[allow(non_snake_case)]
+#[proc_macro_error]
+#[deprecated(since = "0.8.1", note = "Use `MultihashDigest` derive instead.")]
+pub fn Multihash(i: TokenStream) -> TokenStream {
+    match parse::<DeriveInput>(i) {
+        Ok(p) => match Structure::try_new(&p) {
+            Ok(s) => multihash::multihash(s).into_stream(),
+            Err(e) => e.to_compile_error().into(),
+        },
+        Err(e) => e.to_compile_error().into(),
+    }
+}
+
+#[proc_macro_derive(MultihashDigest, attributes(mh))]
+#[allow(non_snake_case)]
+#[proc_macro_error]
+pub fn MultihashDigest(i: TokenStream) -> TokenStream {
+    #[allow(deprecated)]
+    Multihash(i)
+}
diff --git a/derive/src/multihash.rs b/derive-impl/src/multihash.rs
similarity index 98%
rename from derive/src/multihash.rs
rename to derive-impl/src/multihash.rs
index b964e633..237c57d0 100644
--- a/derive/src/multihash.rs
+++ b/derive-impl/src/multihash.rs
@@ -198,7 +198,7 @@ fn error_code_duplicates(hashes: &[Hash]) {
 struct ParseError(Span);
 
 pub fn multihash(s: Structure) -> TokenStream {
-    let mh_crate = match utils::use_crate("multihash") {
+    let mh_crate = match utils::use_crate("multihash-derive") {
         Ok(ident) => ident,
         Err(e) => {
             let err = syn::Error::new(Span::call_site(), e).to_compile_error();
@@ -247,12 +247,12 @@ pub fn multihash(s: Structure) -> TokenStream {
         }
 
         impl core::convert::TryFrom<u64> for #code_enum {
-            type Error = #mh_crate::Error;
+            type Error = #mh_crate::UnsupportedCode;
 
             fn try_from(code: u64) -> Result<Self, Self::Error> {
                 match code {
                     #(#code_from_u64,)*
-                    _ => Err(#mh_crate::Error::unsupported_code(code))
+                    _ => Err(#mh_crate::UnsupportedCode(code))
                 }
             }
         }
diff --git a/derive/src/utils.rs b/derive-impl/src/utils.rs
similarity index 100%
rename from derive/src/utils.rs
rename to derive-impl/src/utils.rs
diff --git a/derive/Cargo.toml b/derive/Cargo.toml
index b59e8ba7..d2172fa2 100644
--- a/derive/Cargo.toml
+++ b/derive/Cargo.toml
@@ -8,21 +8,6 @@ license = "MIT"
 repository = "https://github.com/multiformats/multihash"
 resolver = "2"
 
-[lib]
-proc-macro = true
-
 [dependencies]
-proc-macro2 = { version = "1.0.24", features = ["span-locations"] }
-proc-macro-crate = "~1.1.0"
-proc-macro-error = "1.0.4"
-quote = "1.0.7"
-syn = "1.0.42"
-synstructure = "0.12.4"
-
-[features]
-default = ["std"]
-std = []
-
-[dev-dependencies]
-pretty_assertions = "1.0.0"
-#multihash = { path = "..", default-features = false, features = ["derive", "sha2"] }
+multihash-derive-impl = { version = "0.1.0", path = "../derive-impl" }
+multihash = { version = "0.18.0", path = "../" }
diff --git a/src/hasher.rs b/derive/src/hasher.rs
similarity index 100%
rename from src/hasher.rs
rename to derive/src/hasher.rs
diff --git a/derive/src/lib.rs b/derive/src/lib.rs
index 4c990ee3..74c7560e 100644
--- a/derive/src/lib.rs
+++ b/derive/src/lib.rs
@@ -33,34 +33,69 @@
 //! let hash = Code::Foo.digest(b"hello world!");
 //! println!("{:02x?}", hash);
 //! ```
-extern crate proc_macro;
 
-mod multihash;
-mod utils;
+mod hasher;
 
-use proc_macro::TokenStream;
-use proc_macro_error::proc_macro_error;
-use synstructure::macros::{parse, DeriveInput};
-use synstructure::{MacroResult, Structure};
+use std::convert::TryFrom;
+use std::fmt;
 
-#[proc_macro_derive(Multihash, attributes(mh))]
-#[allow(non_snake_case)]
-#[proc_macro_error]
-#[deprecated(since = "0.8.1", note = "Use `MultihashDigest` derive instead.")]
-pub fn Multihash(i: TokenStream) -> TokenStream {
-    match parse::<DeriveInput>(i) {
-        Ok(p) => match Structure::try_new(&p) {
-            Ok(s) => multihash::multihash(s).into_stream(),
-            Err(e) => e.to_compile_error().into(),
-        },
-        Err(e) => e.to_compile_error().into(),
+pub use hasher::Hasher;
+pub use multihash_derive_impl::MultihashDigest;
+
+pub use multihash::*;
+
+/// The given code is not supported by this codetable.
+#[derive(Debug)]
+pub struct UnsupportedCode(pub u64);
+
+impl fmt::Display for UnsupportedCode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "the code {} is not supported by this codetable", self.0)
     }
 }
 
-#[proc_macro_derive(MultihashDigest, attributes(mh))]
-#[allow(non_snake_case)]
-#[proc_macro_error]
-pub fn MultihashDigest(i: TokenStream) -> TokenStream {
-    #[allow(deprecated)]
-    Multihash(i)
+impl std::error::Error for UnsupportedCode {}
+
+/// Trait that implements hashing.
+///
+/// It is usually implemented by a custom code table enum that derives the [`Multihash` derive].
+///
+/// [`Multihash` derive]: crate::derive
+pub trait MultihashDigest<const S: usize>:
+    TryFrom<u64, Error = UnsupportedCode>
+    + Into<u64>
+    + Send
+    + Sync
+    + Unpin
+    + Copy
+    + Eq
+    + fmt::Debug
+    + 'static
+{
+    /// Calculate the hash of some input data.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// // `Code` implements `MultihashDigest`
+    /// use multihash::{Code, MultihashDigest};
+    ///
+    /// let hash = Code::Sha3_256.digest(b"Hello world!");
+    /// println!("{:02x?}", hash);
+    /// ```
+    fn digest(&self, input: &[u8]) -> Multihash<S>;
+
+    /// Create a multihash from an existing multihash digest.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use multihash::{Code, Hasher, MultihashDigest, Sha3_256};
+    ///
+    /// let mut hasher = Sha3_256::default();
+    /// hasher.update(b"Hello world!");
+    /// let hash = Code::Sha3_256.wrap(&hasher.finalize()).unwrap();
+    /// println!("{:02x?}", hash);
+    /// ```
+    fn wrap(&self, digest: &[u8]) -> std::result::Result<Multihash<S>, multihash::Error>;
 }
diff --git a/src/error.rs b/src/error.rs
index 815ac775..f8df7bc6 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -12,14 +12,6 @@ pub struct Error {
 }
 
 impl Error {
-    /// The specified code is not supported by code table.
-    /// FIXME: This should not be in our public API because it is only needed by the custom derive which we have no knowledge of in this crate.
-    pub fn unsupported_code(code: u64) -> Self {
-        Self {
-            kind: Kind::UnsupportedCode(code),
-        }
-    }
-
     pub(crate) const fn invalid_size(size: u64) -> Self {
         Self {
             kind: Kind::InvalidSize(size),
@@ -51,8 +43,6 @@ impl core::fmt::Display for Error {
 enum Kind {
     /// Io error.
     Io(io::Error),
-    /// Unsupported multihash code.
-    UnsupportedCode(u64),
     /// Invalid multihash size.
     InvalidSize(u64),
     /// Invalid varint.
@@ -80,7 +70,6 @@ impl core::fmt::Display for Kind {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         match self {
             Self::Io(err) => write!(f, "{err}"),
-            Self::UnsupportedCode(code) => write!(f, "Unsupported multihash code {code}."),
             Self::InvalidSize(size) => write!(f, "Invalid multihash size {size}."),
             Self::Varint(err) => write!(f, "{err}"),
         }
@@ -91,7 +80,6 @@ impl StdError for Error {
     fn source(&self) -> Option<&(dyn StdError + 'static)> {
         match &self.kind {
             Kind::Io(inner) => Some(inner),
-            Kind::UnsupportedCode(_) => None,
             Kind::InvalidSize(_) => None,
             Kind::Varint(_) => None, // FIXME: Does not implement `core2::Error`.
         }
diff --git a/src/lib.rs b/src/lib.rs
index 42314b32..7ebe7dfd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -59,7 +59,6 @@ extern crate core;
 #[cfg(any(test, feature = "arb"))]
 mod arb;
 mod error;
-mod hasher;
 mod multihash;
 
 /// Multihash result.
@@ -67,10 +66,7 @@ mod multihash;
 pub type Result<T> = core::result::Result<T, Error>;
 
 pub use crate::error::Error;
-pub use crate::multihash::{Multihash, MultihashDigest};
-pub use hasher::Hasher;
-#[cfg(feature = "derive")]
-pub use multihash_derive as derive;
+pub use crate::multihash::Multihash;
 
 /// Deprecated type-alias for the [`Multihash`] type.
 #[deprecated(since = "0.18.0", note = "Use `multihash::Multihash instead.")]
diff --git a/src/multihash.rs b/src/multihash.rs
index 86491784..d90d1bdd 100644
--- a/src/multihash.rs
+++ b/src/multihash.rs
@@ -1,7 +1,6 @@
 use crate::Error;
 #[cfg(feature = "alloc")]
 use alloc::vec::Vec;
-use core::convert::TryFrom;
 
 use core::convert::TryInto;
 use core::fmt::Debug;
@@ -14,42 +13,6 @@ use std::io;
 #[cfg(not(feature = "std"))]
 use core2::io;
 
-/// Trait that implements hashing.
-///
-/// It is usually implemented by a custom code table enum that derives the [`Multihash` derive].
-///
-/// [`Multihash` derive]: crate::derive
-pub trait MultihashDigest<const S: usize>:
-    TryFrom<u64> + Into<u64> + Send + Sync + Unpin + Copy + Eq + Debug + 'static
-{
-    /// Calculate the hash of some input data.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// // `Code` implements `MultihashDigest`
-    /// use multihash::{Code, MultihashDigest};
-    ///
-    /// let hash = Code::Sha3_256.digest(b"Hello world!");
-    /// println!("{:02x?}", hash);
-    /// ```
-    fn digest(&self, input: &[u8]) -> Multihash<S>;
-
-    /// Create a multihash from an existing multihash digest.
-    ///
-    /// # Example
-    ///
-    /// ```
-    /// use multihash::{Code, Hasher, MultihashDigest, Sha3_256};
-    ///
-    /// let mut hasher = Sha3_256::default();
-    /// hasher.update(b"Hello world!");
-    /// let hash = Code::Sha3_256.wrap(&hasher.finalize()).unwrap();
-    /// println!("{:02x?}", hash);
-    /// ```
-    fn wrap(&self, digest: &[u8]) -> Result<Multihash<S>, Error>;
-}
-
 /// A Multihash instance that only supports the basic functionality and no hashing.
 ///
 /// With this Multihash implementation you can operate on Multihashes in a generic way, but