diff --git a/Cargo.toml b/Cargo.toml
index 8436323..9edab6b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,6 +2,7 @@
 members = [
     "cqrs",
     "cqrs-codegen",
+    "cqrs-codegen/impl",
     "cqrs-core",
     "cqrs-postgres",
     "cqrs-proptest",
diff --git a/cqrs-codegen/.gitignore b/cqrs-codegen/.gitignore
new file mode 100644
index 0000000..edc25b1
--- /dev/null
+++ b/cqrs-codegen/.gitignore
@@ -0,0 +1 @@
+/.watch-cqrs-codegen-impl
diff --git a/cqrs-codegen/Cargo.toml b/cqrs-codegen/Cargo.toml
index f8ce58c..8368c01 100644
--- a/cqrs-codegen/Cargo.toml
+++ b/cqrs-codegen/Cargo.toml
@@ -3,7 +3,7 @@ name = "cqrs-codegen"
 version = "0.1.0-dev"
 edition = "2018"
 # authors =
-description = "Code generation for CQRS/ES"
+description = "Code generation interface for CQRS/ES"
 # license = "Apache-2.0"
 readme = "../README.md"
 # documentation = "https://docs.rs/cqrs-core"
@@ -12,11 +12,14 @@ readme = "../README.md"
 [lib]
 proc-macro = true
 
+[features]
+default = ["watt"]
+no-watt = ["cqrs-codegen-impl", "syn"]
+
 [dependencies]
-proc-macro2 = "1.0.6"
-quote = "1.0.2"
-syn = "1.0.6"
-synstructure = "0.12.1"
+cqrs-codegen-impl = { version = "0.1.0-dev", path = "./impl", optional = true }
+syn = { version = "1.0.7", optional = true }
+watt = { version = "0.3.0", optional = true }
 
 [dev-dependencies]
 cqrs = { version = "0.3", path = "../cqrs" }
diff --git a/cqrs-codegen/build.rs b/cqrs-codegen/build.rs
new file mode 100644
index 0000000..79ba6df
--- /dev/null
+++ b/cqrs-codegen/build.rs
@@ -0,0 +1,147 @@
+use std::{
+    env,
+    error::Error,
+    fs::{self, OpenOptions},
+    io::Write as _,
+    path::Path,
+    process,
+};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let watt = env::var("CARGO_FEATURE_WATT");
+    let no_watt = env::var("CARGO_FEATURE_NO_WATT");
+
+    if watt.is_ok() && no_watt.is_ok() {
+        panic!(
+            "Both 'watt' and 'no-watt' features specified; \
+             exactly one of the two features have to be specified",
+        );
+    } else if watt.is_err() && no_watt.is_err() {
+        panic!(
+            "Neither 'watt', nor 'no-watt' feature specified; \
+             exactly one of the two features have to be specified",
+        );
+    }
+
+    if no_watt.is_ok() {
+        return Ok(());
+    }
+
+    let codegen_wasm_exists = Path::new("./src/codegen.wasm").is_file();
+    let impl_exists = Path::new("./impl").is_dir();
+
+    if !codegen_wasm_exists && !impl_exists {
+        panic!(
+            "Neither './src/codegen.wasm' file, nor './impl/' directory exist, \
+             so it's impossible to build cqrs-codegen with 'watt' feature",
+        );
+    }
+
+    let watch = Path::new("./.watch-cqrs-codegen-impl").exists();
+
+    if watch {
+        if impl_exists {
+            // Have to explicitly exclude 'codegen.wasm', cause otherwise each
+            // rebuild triggers 'rerun-if-changed' and forces rebuild on next
+            // run (which triggers 'rerun-if-changed'...).
+            rerun_if_changed_recursive_with_exceptions("./src", &["codegen.wasm"])?;
+            rerun_if_changed_recursive("./impl/src")?;
+        } else {
+            println!(
+                "cargo:warning='./.watch-cqrs-codegen-impl' file exists, \
+                 but './impl/' directory doesn't; \
+                 './src/codegen.wasm' won't be rebuilt",
+            );
+        }
+    }
+
+    if (!codegen_wasm_exists || watch) && impl_exists {
+        let root = env::current_dir()?;
+
+        env::set_current_dir("./impl")?;
+
+        fs::copy("./Cargo.toml", "./Cargo.toml.orig")?;
+
+        writeln!(
+            OpenOptions::new().append(true).open("./Cargo.toml")?,
+            "[workspace]",
+        )?;
+
+        let status = process::Command::new(env::var("CARGO")?)
+            .args(&[
+                "build",
+                "--release",
+                "--target",
+                "wasm32-unknown-unknown",
+                "--features",
+                "watt",
+                "--target-dir",
+                "target",
+            ])
+            .status()?;
+
+        if !status.success() {
+            panic!(
+                "cargo-build for cqrs-codegen-impl returned \
+                 non-zero status code",
+            );
+        }
+
+        fs::copy("./Cargo.toml.orig", "./Cargo.toml")?;
+
+        // Removing ./Cargo.toml.orig is not critical,
+        // so result is explicitly ignored.
+        drop(fs::remove_file("./Cargo.toml.orig"));
+
+        env::set_current_dir(root)?;
+
+        fs::copy(
+            "./impl/target/wasm32-unknown-unknown/release/cqrs_codegen_impl.wasm",
+            "./src/codegen.wasm",
+        )?;
+    }
+
+    Ok(())
+}
+
+fn rerun_if_changed(path: &str) {
+    println!("cargo:rerun-if-changed={}", path);
+}
+
+fn rerun_if_changed_recursive<P>(path: P) -> Result<(), Box<dyn Error>>
+where
+    P: AsRef<Path>,
+{
+    rerun_if_changed_recursive_with_exceptions(path, &[])
+}
+
+fn rerun_if_changed_recursive_with_exceptions<P>(
+    path: P,
+    exceptions: &[&str],
+) -> Result<(), Box<dyn Error>>
+where
+    P: AsRef<Path>,
+{
+    for path in fs::read_dir(path)? {
+        let path = path?;
+
+        if exceptions
+            .iter()
+            .any(|&exception| path.file_name() == exception)
+        {
+            continue;
+        }
+
+        let path_type = path.file_type()?;
+
+        let path = path.path();
+
+        if path_type.is_dir() {
+            rerun_if_changed_recursive(path)?;
+        } else if path_type.is_file() {
+            rerun_if_changed(path.to_str().ok_or("Failed to convert PathBuf to &str")?);
+        }
+    }
+
+    Ok(())
+}
diff --git a/cqrs-codegen/impl/.gitignore b/cqrs-codegen/impl/.gitignore
new file mode 100644
index 0000000..042776a
--- /dev/null
+++ b/cqrs-codegen/impl/.gitignore
@@ -0,0 +1,2 @@
+/Cargo.lock
+/target/
diff --git a/cqrs-codegen/impl/Cargo.toml b/cqrs-codegen/impl/Cargo.toml
new file mode 100644
index 0000000..d5e986e
--- /dev/null
+++ b/cqrs-codegen/impl/Cargo.toml
@@ -0,0 +1,26 @@
+[package]
+name = "cqrs-codegen-impl"
+version = "0.1.0-dev"
+edition = "2018"
+# authors =
+description = "Code generation implementation for CQRS/ES"
+# license = "Apache-2.0"
+readme = "../README.md"
+# documentation = "https://docs.rs/cqrs-core"
+# repository = "/~https://github.com/cq-rs/cqrs"
+
+[lib]
+crate-type = ["rlib", "cdylib"]
+
+[features]
+default = []
+watt = []
+
+[dependencies]
+proc-macro2 = "1.0.6"
+quote = "1.0.2"
+syn = "1.0.6"
+synstructure = { git = "/~https://github.com/ffuugoo/synstructure", default-features = false }
+
+[patch.crates-io]
+proc-macro2 = { git = "/~https://github.com/dtolnay/watt" }
diff --git a/cqrs-codegen/src/event/event.rs b/cqrs-codegen/impl/src/event/event.rs
similarity index 100%
rename from cqrs-codegen/src/event/event.rs
rename to cqrs-codegen/impl/src/event/event.rs
diff --git a/cqrs-codegen/src/event/mod.rs b/cqrs-codegen/impl/src/event/mod.rs
similarity index 97%
rename from cqrs-codegen/src/event/mod.rs
rename to cqrs-codegen/impl/src/event/mod.rs
index afde654..13fb158 100644
--- a/cqrs-codegen/src/event/mod.rs
+++ b/cqrs-codegen/impl/src/event/mod.rs
@@ -12,9 +12,9 @@ use synstructure::Structure;
 
 use crate::util::{self, TryInto as _};
 
-pub(crate) use event::derive;
-pub(crate) use registered_event::derive as registered_derive;
-pub(crate) use versioned_event::derive as versioned_derive;
+pub use event::derive as event_derive;
+pub use registered_event::derive as registered_event_derive;
+pub use versioned_event::derive as versioned_event_derive;
 
 /// Name of the attribute, used for this family of derives.
 const ATTR_NAME: &str = "event";
diff --git a/cqrs-codegen/src/event/registered_event.rs b/cqrs-codegen/impl/src/event/registered_event.rs
similarity index 97%
rename from cqrs-codegen/src/event/registered_event.rs
rename to cqrs-codegen/impl/src/event/registered_event.rs
index e66b12f..264f47f 100644
--- a/cqrs-codegen/src/event/registered_event.rs
+++ b/cqrs-codegen/impl/src/event/registered_event.rs
@@ -30,6 +30,8 @@ fn derive_struct(input: syn::DeriveInput) -> Result<proc_macro2::TokenStream> {
 /// Implements [`crate::derive_registered_event`] macro expansion for enums
 /// via [`synstructure`].
 fn derive_enum(input: syn::DeriveInput) -> Result<proc_macro2::TokenStream> {
+    util::assert_attr_does_not_exist(&input.attrs, super::ATTR_NAME)?;
+
     let mut structure = Structure::try_new(&input)?;
 
     super::render_enum_proxy_method_calls(
diff --git a/cqrs-codegen/src/event/versioned_event.rs b/cqrs-codegen/impl/src/event/versioned_event.rs
similarity index 100%
rename from cqrs-codegen/src/event/versioned_event.rs
rename to cqrs-codegen/impl/src/event/versioned_event.rs
diff --git a/cqrs-codegen/impl/src/lib.rs b/cqrs-codegen/impl/src/lib.rs
new file mode 100644
index 0000000..ae9a433
--- /dev/null
+++ b/cqrs-codegen/impl/src/lib.rs
@@ -0,0 +1,38 @@
+mod event;
+mod util;
+
+use proc_macro2::TokenStream;
+
+#[cfg(not(feature = "watt"))]
+/// Re-exports proc macro `$fn` as is.
+macro_rules! export {
+    ($fn:ident) => {
+        pub use event::$fn;
+    };
+}
+
+#[cfg(feature = "watt")]
+/// Re-exports proc macro `$fn` via WASM ABI.
+macro_rules! export {
+    ($fn:ident) => {
+        #[no_mangle]
+        pub extern "C" fn $fn(input: TokenStream) -> TokenStream {
+            expand(syn::parse2(input), event::$fn)
+        }
+    };
+}
+
+/// Performs expansion of a given proc macro implementation.
+pub fn expand<TS: From<TokenStream>>(
+    input: syn::Result<syn::DeriveInput>,
+    macro_impl: fn(syn::DeriveInput) -> syn::Result<TokenStream>,
+) -> TS {
+    match input.and_then(|input| macro_impl(input)) {
+        Ok(res) => res.into(),
+        Err(err) => err.to_compile_error().into(),
+    }
+}
+
+export!(event_derive);
+export!(registered_event_derive);
+export!(versioned_event_derive);
diff --git a/cqrs-codegen/src/util.rs b/cqrs-codegen/impl/src/util.rs
similarity index 100%
rename from cqrs-codegen/src/util.rs
rename to cqrs-codegen/impl/src/util.rs
diff --git a/cqrs-codegen/src/codegen.wasm b/cqrs-codegen/src/codegen.wasm
new file mode 100755
index 0000000..648ea57
Binary files /dev/null and b/cqrs-codegen/src/codegen.wasm differ
diff --git a/cqrs-codegen/src/lib.rs b/cqrs-codegen/src/lib.rs
index 47cb107..66199b7 100644
--- a/cqrs-codegen/src/lib.rs
+++ b/cqrs-codegen/src/lib.rs
@@ -1,10 +1,31 @@
 extern crate proc_macro;
 
-mod event;
-mod util;
-
 use proc_macro::TokenStream;
-use syn::parse::Result;
+
+#[cfg(all(not(feature = "watt"), feature = "no-watt"))]
+/// Imports proc macro from implementation crate as is.
+macro_rules! import {
+    ($input:expr, $fn:ident) => {
+        cqrs_codegen_impl::expand(syn::parse($input), cqrs_codegen_impl::$fn)
+    };
+}
+
+#[cfg(all(feature = "watt", not(feature = "no-watt")))]
+/// Imports proc macro from implementation crate via WASM ABI.
+macro_rules! import {
+    ($input:expr, $fn:ident) => {
+        wasm::MACRO.proc_macro(stringify!($fn), $input)
+    };
+}
+
+#[cfg(all(feature = "watt", not(feature = "no-watt")))]
+mod wasm {
+    /// Generated WASM of implementation crate.
+    static WASM: &[u8] = include_bytes!("codegen.wasm");
+
+    /// Callable interface of the generated [`WASM`].
+    pub static MACRO: watt::WasmMacro = watt::WasmMacro::new(WASM);
+}
 
 /// Derives [`cqrs::Event`] implementation for structs and enums.
 ///
@@ -48,8 +69,8 @@ use syn::parse::Result;
 /// }
 /// ```
 #[proc_macro_derive(Event, attributes(event))]
-pub fn derive_event(input: TokenStream) -> TokenStream {
-    expand(input, event::derive)
+pub fn event_derive(input: TokenStream) -> TokenStream {
+    import!(input, event_derive)
 }
 
 /// Derives [`cqrs::RegisteredEvent`] implementation for structs and enums.
@@ -92,8 +113,8 @@ pub fn derive_event(input: TokenStream) -> TokenStream {
 /// }
 /// ```
 #[proc_macro_derive(RegisteredEvent)]
-pub fn derive_registered_event(input: TokenStream) -> TokenStream {
-    expand(input, event::registered_derive)
+pub fn registered_event_derive(input: TokenStream) -> TokenStream {
+    import!(input, registered_event_derive)
 }
 
 /// Derives [`cqrs::VersionedEvent`] implementation for structs and enums.
@@ -138,16 +159,6 @@ pub fn derive_registered_event(input: TokenStream) -> TokenStream {
 /// }
 /// ```
 #[proc_macro_derive(VersionedEvent, attributes(event))]
-pub fn derive_versioned_event(input: TokenStream) -> TokenStream {
-    expand(input, event::versioned_derive)
-}
-
-type MacroImpl = fn(syn::DeriveInput) -> Result<proc_macro2::TokenStream>;
-
-/// Expands given input [`TokenStream`] with a given macro implementation.
-fn expand(input: TokenStream, macro_impl: MacroImpl) -> TokenStream {
-    match syn::parse(input).and_then(|i| macro_impl(i)) {
-        Ok(res) => res.into(),
-        Err(err) => err.to_compile_error().into(),
-    }
+pub fn versioned_event_derive(input: TokenStream) -> TokenStream {
+    import!(input, versioned_event_derive)
 }