diff --git a/codegen/Cargo.toml b/codegen/Cargo.toml
index 79a179b1..67baf653 100644
--- a/codegen/Cargo.toml
+++ b/codegen/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "rhai_codegen"
-version = "1.3.0"
+version = "1.4.0"
 edition = "2018"
 authors = ["jhwgh1968", "Stephen Chung"]
 description = "Procedural macros support package for Rhai, a scripting language and engine for Rust"
diff --git a/codegen/src/module.rs b/codegen/src/module.rs
index c25a102d..bafd1b33 100644
--- a/codegen/src/module.rs
+++ b/codegen/src/module.rs
@@ -10,7 +10,7 @@ use std::borrow::Cow;
 
 use crate::attrs::{AttrItem, ExportInfo, ExportScope, ExportedParams};
 use crate::function::ExportedFn;
-use crate::rhai_module::ExportedConst;
+use crate::rhai_module::{ExportedConst, ExportedType};
 
 #[derive(Debug, Clone, Eq, PartialEq, Hash, Default)]
 pub struct ExportedModParams {
@@ -89,8 +89,9 @@ impl ExportedParams for ExportedModParams {
 #[derive(Debug)]
 pub struct Module {
     mod_all: syn::ItemMod,
-    fns: Vec<ExportedFn>,
     consts: Vec<ExportedConst>,
+    custom_types: Vec<ExportedType>,
+    fns: Vec<ExportedFn>,
     sub_modules: Vec<Module>,
     params: ExportedModParams,
 }
@@ -107,6 +108,7 @@ impl Parse for Module {
         let mut mod_all: syn::ItemMod = input.parse()?;
         let fns: Vec<_>;
         let mut consts = Vec::new();
+        let mut custom_types = Vec::new();
         let mut sub_modules = Vec::new();
 
         if let Some((.., ref mut content)) = mod_all.content {
@@ -155,6 +157,25 @@ impl Parse for Module {
                     _ => {}
                 }
             }
+            // Gather and parse type definitions.
+            for item in content.iter() {
+                match item {
+                    syn::Item::Type(syn::ItemType {
+                        vis,
+                        ident,
+                        attrs,
+                        ty,
+                        ..
+                    }) if matches!(vis, syn::Visibility::Public(..)) => {
+                        custom_types.push(ExportedType {
+                            name: ident.to_string(),
+                            typ: ty.clone(),
+                            cfg_attrs: crate::attrs::collect_cfg_attr(&attrs),
+                        })
+                    }
+                    _ => {}
+                }
+            }
             // Gather and parse sub-module definitions.
             //
             // They are actually removed from the module's body, because they will need
@@ -188,6 +209,7 @@ impl Parse for Module {
             mod_all,
             fns,
             consts,
+            custom_types,
             sub_modules,
             params: ExportedModParams::default(),
         })
@@ -241,6 +263,7 @@ impl Module {
             mut mod_all,
             mut fns,
             consts,
+            custom_types,
             mut sub_modules,
             params,
             ..
@@ -257,6 +280,7 @@ impl Module {
             let mod_gen = crate::rhai_module::generate_body(
                 &mut fns,
                 &consts,
+                &custom_types,
                 &mut sub_modules,
                 &params.scope,
             );
@@ -300,6 +324,11 @@ impl Module {
         &self.consts
     }
 
+    #[allow(dead_code)]
+    pub fn custom_types(&self) -> &[ExportedType] {
+        &self.custom_types
+    }
+
     #[allow(dead_code)]
     pub fn fns(&self) -> &[ExportedFn] {
         &self.fns
diff --git a/codegen/src/rhai_module.rs b/codegen/src/rhai_module.rs
index e3fd07af..ccd40601 100644
--- a/codegen/src/rhai_module.rs
+++ b/codegen/src/rhai_module.rs
@@ -18,9 +18,17 @@ pub struct ExportedConst {
     pub cfg_attrs: Vec<syn::Attribute>,
 }
 
+#[derive(Debug)]
+pub struct ExportedType {
+    pub name: String,
+    pub typ: Box<syn::Type>,
+    pub cfg_attrs: Vec<syn::Attribute>,
+}
+
 pub fn generate_body(
     fns: &mut [ExportedFn],
     consts: &[ExportedConst],
+    custom_types: &[ExportedType],
     sub_modules: &mut [Module],
     parent_scope: &ExportScope,
 ) -> TokenStream {
@@ -54,6 +62,29 @@ pub fn generate_body(
         );
     }
 
+    for ExportedType {
+        name,
+        typ,
+        cfg_attrs,
+        ..
+    } in custom_types
+    {
+        let const_literal = syn::LitStr::new(&name, Span::call_site());
+
+        let cfg_attrs: Vec<_> = cfg_attrs
+            .iter()
+            .map(syn::Attribute::to_token_stream)
+            .collect();
+
+        set_const_statements.push(
+            syn::parse2::<syn::Stmt>(quote! {
+                #(#cfg_attrs)*
+                m.set_custom_type::<#typ>(#const_literal);
+            })
+            .unwrap(),
+        );
+    }
+
     for item_mod in sub_modules {
         item_mod.update_scope(&parent_scope);
         if item_mod.skipped() {
diff --git a/codegen/src/test/module.rs b/codegen/src/test/module.rs
index f4700e83..be9b93e5 100644
--- a/codegen/src/test/module.rs
+++ b/codegen/src/test/module.rs
@@ -37,6 +37,31 @@ mod module_tests {
         );
     }
 
+    #[test]
+    fn one_factory_fn_with_custom_type_module() {
+        let input_tokens: TokenStream = quote! {
+            pub mod one_fn {
+                pub type Hello = ();
+
+                pub fn get_mystic_number() -> INT {
+                    42
+                }
+            }
+        };
+
+        let item_mod = syn::parse2::<Module>(input_tokens).unwrap();
+        assert!(item_mod.consts().is_empty());
+        assert_eq!(item_mod.custom_types().len(), 1);
+        assert_eq!(item_mod.custom_types()[0].name.to_string(), "Hello");
+        assert_eq!(item_mod.fns().len(), 1);
+        assert_eq!(item_mod.fns()[0].name().to_string(), "get_mystic_number");
+        assert_eq!(item_mod.fns()[0].arg_count(), 0);
+        assert_eq!(
+            item_mod.fns()[0].return_type().unwrap(),
+            &syn::parse2::<syn::Type>(quote! { INT }).unwrap()
+        );
+    }
+
     #[test]
     #[cfg(feature = "metadata")]
     fn one_factory_fn_with_comments_module() {
@@ -753,7 +778,13 @@ mod generate_tests {
                 #[derive(Debug, Clone)]
                 pub struct Foo(pub INT);
 
+                pub type Hello = Foo;
+
                 pub const MYSTIC_NUMBER: Foo = Foo(42);
+
+                pub fn get_mystic_number(x: &mut Hello) -> INT {
+                    x.0
+                }
             }
         };
 
@@ -762,7 +793,13 @@ mod generate_tests {
                 #[derive(Debug, Clone)]
                 pub struct Foo(pub INT);
 
+                pub type Hello = Foo;
+
                 pub const MYSTIC_NUMBER: Foo = Foo(42);
+
+                pub fn get_mystic_number(x: &mut Hello) -> INT {
+                    x.0
+                }
                 #[allow(unused_imports)]
                 use super::*;
 
@@ -774,9 +811,32 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
+                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public,
+                             Some(get_mystic_number_token::PARAM_NAMES), &[TypeId::of::<Hello>()],
+                             get_mystic_number_token().into());
                     m.set_var("MYSTIC_NUMBER", MYSTIC_NUMBER);
+                    m.set_custom_type::<Foo>("Hello");
                     if flatten {} else {}
                 }
+
+                #[allow(non_camel_case_types)]
+                pub struct get_mystic_number_token();
+                impl get_mystic_number_token {
+                    pub const PARAM_NAMES: &'static [&'static str] = &["x: &mut Hello", "INT"];
+                    #[inline(always)] pub fn param_types() -> [TypeId; 1usize] { [TypeId::of::<Hello>()] }
+                }
+                impl PluginFunction for get_mystic_number_token {
+                    #[inline(always)]
+                    fn call(&self, context: NativeCallContext, args: &mut [&mut Dynamic]) -> RhaiResult {
+                        if args[0usize].is_read_only() {
+                            return Err(EvalAltResult::ErrorAssignmentToConstant("x".to_string(), Position::NONE).into());
+                        }
+                        let arg0 = &mut args[0usize].write_lock::<Hello>().unwrap();
+                        Ok(Dynamic::from(get_mystic_number(arg0)))
+                    }
+
+                    #[inline(always)] fn is_method_call(&self) -> bool { true }
+                }
             }
         };
 
diff --git a/src/api/register.rs b/src/api/register.rs
index 72720c7a..1d5220d5 100644
--- a/src/api/register.rs
+++ b/src/api/register.rs
@@ -10,7 +10,7 @@ use std::any::{type_name, TypeId};
 use std::prelude::v1::*;
 
 impl Engine {
-    /// Get the global namespace module (which is the last module in `global_modules`).
+    /// Get the global namespace module (which is the fist module in `global_modules`).
     #[inline(always)]
     #[allow(dead_code)]
     pub(crate) fn global_namespace(&self) -> &Module {
@@ -273,7 +273,8 @@ impl Engine {
     /// ```
     #[inline(always)]
     pub fn register_type_with_name<T: Variant + Clone>(&mut self, name: &str) -> &mut Self {
-        self.register_type_with_name_raw(type_name::<T>(), name)
+        self.custom_types.add_type::<T>(name);
+        self
     }
     /// Register a custom type for use with the [`Engine`], with a pretty-print name
     /// for the `type_of` function. The type must implement [`Clone`].
@@ -288,8 +289,7 @@ impl Engine {
         name: impl Into<Identifier>,
     ) -> &mut Self {
         // Add the pretty-print type name into the map
-        self.type_names
-            .insert(fully_qualified_type_path.into(), name.into());
+        self.custom_types.add(fully_qualified_type_path, name);
         self
     }
     /// Register an type iterator for an iterable type with the [`Engine`].
diff --git a/src/api/type_names.rs b/src/api/type_names.rs
index 3edb1c3b..bf9ac7da 100644
--- a/src/api/type_names.rs
+++ b/src/api/type_names.rs
@@ -85,9 +85,15 @@ impl Engine {
     #[inline]
     #[must_use]
     pub fn map_type_name<'a>(&'a self, name: &'a str) -> &'a str {
-        self.type_names
-            .get(name)
-            .map(|s| s.as_str())
+        self.global_modules
+            .iter()
+            .find_map(|m| m.get_custom_type(name))
+            .or_else(|| {
+                self.global_sub_modules
+                    .iter()
+                    .find_map(|(_, m)| m.get_custom_type(name))
+            })
+            .or_else(|| self.custom_types.get(name))
             .unwrap_or_else(|| map_std_type_name(name, true))
     }
 
@@ -109,9 +115,8 @@ impl Engine {
             };
         }
 
-        self.type_names
+        self.custom_types
             .get(name)
-            .map(|s| s.as_str())
             .unwrap_or_else(|| match name {
                 "INT" => return type_name::<crate::INT>(),
                 #[cfg(not(feature = "no_float"))]
diff --git a/src/engine.rs b/src/engine.rs
index eaefc5dd..f180f624 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -6,7 +6,7 @@ use crate::func::native::{
 };
 use crate::packages::{Package, StandardPackage};
 use crate::tokenizer::Token;
-use crate::types::dynamic::Union;
+use crate::types::{dynamic::Union, CustomTypesCollection};
 use crate::{
     Dynamic, Identifier, ImmutableString, Module, OptimizationLevel, Position, RhaiResult, Shared,
     StaticVec,
@@ -105,7 +105,7 @@ pub struct Engine {
     pub(crate) module_resolver: Option<Box<dyn crate::ModuleResolver>>,
 
     /// A map mapping type names to pretty-print names.
-    pub(crate) type_names: BTreeMap<Identifier, Identifier>,
+    pub(crate) custom_types: CustomTypesCollection,
 
     /// An empty [`ImmutableString`] for cloning purposes.
     pub(crate) empty_string: ImmutableString,
@@ -160,7 +160,7 @@ impl fmt::Debug for Engine {
         f.field("global_sub_modules", &self.global_sub_modules)
             .field("module_resolver", &self.module_resolver.is_some());
 
-        f.field("type_names", &self.type_names)
+        f.field("type_names", &self.custom_types)
             .field("disabled_symbols", &self.disabled_symbols)
             .field("custom_keywords", &self.custom_keywords)
             .field("custom_syntax", &(!self.custom_syntax.is_empty()))
@@ -271,7 +271,7 @@ impl Engine {
             #[cfg(not(feature = "no_module"))]
             module_resolver: None,
 
-            type_names: BTreeMap::new(),
+            custom_types: CustomTypesCollection::new(),
             empty_string: ImmutableString::new(),
             disabled_symbols: BTreeSet::new(),
             custom_keywords: BTreeMap::new(),
diff --git a/src/module/mod.rs b/src/module/mod.rs
index 0491e3e9..a70ee8e9 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -5,7 +5,7 @@ use crate::func::{
     shared_take_or_clone, CallableFunction, FnCallArgs, IteratorFn, RegisterNativeFunction,
     SendSync,
 };
-use crate::types::dynamic::Variant;
+use crate::types::{dynamic::Variant, CustomTypesCollection};
 use crate::{
     calc_fn_params_hash, calc_qualified_fn_hash, combine_hashes, Dynamic, Identifier,
     ImmutableString, NativeCallContext, RhaiResultOf, Shared, StaticVec,
@@ -232,6 +232,8 @@ pub struct Module {
     pub(crate) internal: bool,
     /// Is this module part of a standard library?
     pub(crate) standard: bool,
+    /// Custom types.
+    custom_types: CustomTypesCollection,
     /// Sub-modules.
     modules: BTreeMap<Identifier, Shared<Module>>,
     /// [`Module`] variables.
@@ -339,6 +341,7 @@ impl Module {
             id: Identifier::new_const(),
             internal: false,
             standard: false,
+            custom_types: CustomTypesCollection::new(),
             modules: BTreeMap::new(),
             variables: BTreeMap::new(),
             all_variables: BTreeMap::new(),
@@ -413,6 +416,17 @@ impl Module {
         self
     }
 
+    /// Map a custom type to a friendly display name.
+    #[inline(always)]
+    pub fn set_custom_type<T>(&mut self, name: &str) {
+        self.custom_types.add_type::<T>(name)
+    }
+    /// Get the display name of a registered custom type.
+    #[inline(always)]
+    pub fn get_custom_type(&self, key: &str) -> Option<&str> {
+        self.custom_types.get(key)
+    }
+
     /// Is the [`Module`] empty?
     ///
     /// # Example
diff --git a/src/types/custom_types.rs b/src/types/custom_types.rs
new file mode 100644
index 00000000..e46aaddc
--- /dev/null
+++ b/src/types/custom_types.rs
@@ -0,0 +1,43 @@
+//! Collection of custom types.
+
+use crate::Identifier;
+use std::{any::type_name, collections::BTreeMap, fmt};
+
+/// _(internals)_ A custom type.
+/// Exported under the `internals` feature only.
+pub type CustomType = Identifier;
+
+/// _(internals)_ A collection of custom types.
+/// Exported under the `internals` feature only.
+#[derive(Clone, Hash, Default)]
+pub struct CustomTypesCollection(BTreeMap<Identifier, CustomType>);
+
+impl fmt::Debug for CustomTypesCollection {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("CustomTypesCollection ")?;
+        f.debug_map().entries(self.0.iter()).finish()
+    }
+}
+
+impl CustomTypesCollection {
+    /// Create a new [`CustomTypesCollection`].
+    #[inline(always)]
+    pub fn new() -> Self {
+        Self(BTreeMap::new())
+    }
+    /// Register a custom type.
+    #[inline(always)]
+    pub fn add(&mut self, key: impl Into<Identifier>, name: impl Into<Identifier>) {
+        self.0.insert(key.into(), name.into());
+    }
+    /// Register a custom type.
+    #[inline(always)]
+    pub fn add_type<T>(&mut self, name: &str) {
+        self.0.insert(type_name::<T>().into(), name.into());
+    }
+    /// Find a custom type.
+    #[inline(always)]
+    pub fn get(&self, key: &str) -> Option<&str> {
+        self.0.get(key).map(CustomType::as_str)
+    }
+}
diff --git a/src/types/dynamic.rs b/src/types/dynamic.rs
index 30c05a52..afeb3d7c 100644
--- a/src/types/dynamic.rs
+++ b/src/types/dynamic.rs
@@ -1,4 +1,5 @@
-//! Helper module which defines the [`Any`] trait to to allow dynamic value handling.
+//! Helper module which defines the [`Dynamic`] data type and the
+//! [`Any`] trait to to allow custom type handling.
 
 use crate::func::native::SendSync;
 use crate::{reify, ExclusiveRange, FnPtr, ImmutableString, InclusiveRange, INT};
diff --git a/src/types/mod.rs b/src/types/mod.rs
index 66da654c..6fad549e 100644
--- a/src/types/mod.rs
+++ b/src/types/mod.rs
@@ -1,5 +1,6 @@
 //! Module defining Rhai data types.
 
+pub mod custom_types;
 pub mod dynamic;
 pub mod error;
 pub mod fn_ptr;
@@ -8,6 +9,7 @@ pub mod interner;
 pub mod parse_error;
 pub mod scope;
 
+pub use custom_types::{CustomType, CustomTypesCollection};
 pub use dynamic::Dynamic;
 #[cfg(not(feature = "no_std"))]
 pub use dynamic::Instant;
diff --git a/tests/modules.rs b/tests/modules.rs
index 25e17117..2b952a8d 100644
--- a/tests/modules.rs
+++ b/tests/modules.rs
@@ -53,9 +53,13 @@ fn test_module_sub_module() -> Result<(), Box<EvalAltResult>> {
 
     assert_eq!(m2.get_var_value::<INT>("answer").unwrap(), 41);
 
+    module.set_custom_type::<()>("Don't Panic");
+
     let mut engine = Engine::new();
     engine.register_static_module("question", module.into());
 
+    assert_eq!(engine.eval::<String>("type_of(())")?, "Don't Panic");
+
     assert_eq!(engine.eval::<INT>("question::MYSTIC_NUMBER")?, 42);
     assert!(engine.eval::<INT>("MYSTIC_NUMBER").is_err());
     assert_eq!(engine.eval::<INT>("question::life::universe::answer")?, 41);