diff --git a/lib/rdf.ex b/lib/rdf.ex
index 517cef2..56d1909 100644
--- a/lib/rdf.ex
+++ b/lib/rdf.ex
@@ -209,10 +209,7 @@ defmodule RDF do
   defdelegate literal(value),       to: Literal, as: :new
   defdelegate literal(value, opts), to: Literal, as: :new
 
-  def literal?(%Literal{}), do: true
-  def literal?(%RDF.Literal.Generic{}), do: true
-  def literal?(%datatype{}), do: Literal.Datatype.Registry.datatype?(datatype)
-  def literal?(_), do: false
+  defdelegate literal?(literal), to: Literal.Datatype.Registry
 
   defdelegate triple(s, p, o),  to: Triple, as: :new
   defdelegate triple(tuple),    to: Triple, as: :new
diff --git a/lib/rdf/literal.ex b/lib/rdf/literal.ex
index e0ac7a3..f4960a2 100644
--- a/lib/rdf/literal.ex
+++ b/lib/rdf/literal.ex
@@ -92,12 +92,6 @@ defmodule RDF.Literal do
 
   def coerce(%__MODULE__{} = literal), do: literal
 
-  Enum.each(Datatype.Registry.datatypes(), fn datatype ->
-    def coerce(%unquote(datatype){} = literal) do
-      %__MODULE__{literal: literal}
-    end
-  end)
-
   def coerce(value) when is_binary(value),  do: RDF.XSD.String.new(value)
   def coerce(value) when is_boolean(value), do: RDF.XSD.Boolean.new(value)
   def coerce(value) when is_integer(value), do: RDF.XSD.Integer.new(value)
@@ -108,7 +102,22 @@ defmodule RDF.Literal do
   def coerce(%DateTime{} = value),          do: RDF.XSD.DateTime.new(value)
   def coerce(%NaiveDateTime{} = value),     do: RDF.XSD.DateTime.new(value)
   def coerce(%URI{} = value),               do: RDF.XSD.AnyURI.new(value)
-  def coerce(_),                            do: nil
+
+  # Although the following catch-all-clause for all structs could handle the core datatypes
+  # we're generating dedicated clauses for them here, as they are approx. 15% faster
+  Enum.each(Datatype.Registry.core_datatypes(), fn datatype ->
+    def coerce(%unquote(datatype){} = datatype_literal) do
+      %__MODULE__{literal: datatype_literal}
+    end
+  end)
+
+  def coerce(%_datatype{} = datatype_literal) do
+    if Datatype.Registry.literal?(datatype_literal) do
+      %__MODULE__{literal: datatype_literal}
+    end
+  end
+
+  def coerce(_), do: nil
 
 
   @doc """
diff --git a/lib/rdf/literal/datatype.ex b/lib/rdf/literal/datatype.ex
index da365e9..9fa7027 100644
--- a/lib/rdf/literal/datatype.ex
+++ b/lib/rdf/literal/datatype.ex
@@ -140,6 +140,17 @@ defmodule RDF.Literal.Datatype do
   defmacro __using__(opts) do
     name = Keyword.fetch!(opts, :name)
     id = Keyword.fetch!(opts, :id)
+    do_register = Keyword.get(opts, :register, not is_nil(id))
+    datatype = __CALLER__.module
+
+    # TODO: find an alternative to Code.eval_quoted - We want to support that id can be passed via a function call
+    unquoted_id =
+      if do_register do
+        id
+        |> Code.eval_quoted([], __ENV__)
+        |> elem(0)
+        |> to_string()
+      end
 
     quote do
       @behaviour unquote(__MODULE__)
@@ -258,6 +269,15 @@ defmodule RDF.Literal.Datatype do
           literal.__struct__.lexical(literal)
         end
       end
+
+      if unquote(do_register) do
+        import ProtocolEx
+
+        defimpl_ex Registration, unquote(unquoted_id),
+                   for: RDF.Literal.Datatype.Registry.Registration do
+          def datatype(id), do: unquote(datatype)
+        end
+      end
     end
   end
 end
diff --git a/lib/rdf/literal/datatype/registry.ex b/lib/rdf/literal/datatype/registry.ex
index bf2af7c..6fb00b2 100644
--- a/lib/rdf/literal/datatype/registry.ex
+++ b/lib/rdf/literal/datatype/registry.ex
@@ -1,33 +1,45 @@
-# TODO: This registry should be managed automatically/dynamically and be extendable, to allow user-defined datatypes ...
 defmodule RDF.Literal.Datatype.Registry do
   @moduledoc false
 
   alias RDF.{Literal, IRI, XSD}
+  alias RDF.Literal.Datatype.Registry.Registration
 
-  @datatypes [RDF.LangString | Enum.to_list(XSD.datatypes())]
+  import RDF.Guards
 
-  @mapping Map.new(@datatypes, fn datatype -> {IRI.new(datatype.id), datatype} end)
+  @core_datatypes [RDF.LangString | Enum.to_list(XSD.datatypes())]
+  @mapping Map.new(@core_datatypes, fn datatype -> {IRI.new(datatype.id), datatype} end)
 
   @doc """
-  The mapping of IRIs of datatypes to their `RDF.Literal.Datatype`.
+  The IRIs of all core `RDF.Literal.Datatype`s.
   """
-  @spec mapping :: %{IRI.t => Literal.Datatype.t}
-  def mapping, do: @mapping
+  @spec core_ids :: [IRI.t]
+  def core_ids, do: Map.keys(@mapping)
 
   @doc """
-  The IRIs of all datatypes with a `RDF.Literal.Datatype` defined.
+  All core `RDF.Literal.Datatype` modules.
   """
-  @spec ids :: [IRI.t]
-  def ids, do: Map.keys(@mapping)
+  @spec core_datatypes :: Enum.t
+  def core_datatypes, do: @core_datatypes
 
   @doc """
-  All defined `RDF.Literal.Datatype` modules.
+  Checks if the given module is core datatype.
   """
-  @spec datatypes :: Enum.t
-  def datatypes, do: @datatypes
+  @spec core_datatype?(module) :: boolean
+  def core_datatype?(module), do: module in @core_datatypes
 
+  @doc """
+  Checks if the given module is a core datatype or a registered custom datatype implementing the `RDF.Literal.Datatype` behaviour.
+  """
   @spec datatype?(module) :: boolean
-  def datatype?(module), do: module in @datatypes
+  def datatype?(module) do
+    core_datatype?(module) or implements_datatype_behaviour?(module)
+  end
+
+  @spec literal?(module) :: boolean
+  def literal?(%Literal{}), do: true
+  def literal?(%Literal.Generic{}), do: true
+  def literal?(%datatype{}), do: datatype?(datatype)
+  def literal?(_), do: false
 
   @doc """
   Returns the `RDF.Literal.Datatype` for a directly datatype IRI or the datatype IRI of a `RDF.Literal`.
@@ -35,5 +47,19 @@ defmodule RDF.Literal.Datatype.Registry do
   @spec get(Literal.t | IRI.t | String.t) :: Literal.Datatype.t
   def get(%Literal{} = literal), do: Literal.datatype(literal)
   def get(id) when is_binary(id), do: id |> IRI.new() |> get()
-  def get(id), do: @mapping[id]
+  def get(id) when maybe_ns_term(id), do: id |> IRI.new() |> get()
+  def get(id), do: @mapping[id] || get_custom_datatype(id)
+
+  defp get_custom_datatype(id) do
+    id
+    |> to_string()
+    |> Registration.datatype()
+  end
+
+  defp implements_datatype_behaviour?(module) do
+    module.module_info[:attributes]
+    |> Keyword.get_values(:behaviour)
+    |> List.flatten()
+    |> Enum.member?(RDF.Literal.Datatype)
+  end
 end
diff --git a/lib/rdf/literal/datatype/registry/protocol.ex b/lib/rdf/literal/datatype/registry/protocol.ex
new file mode 100644
index 0000000..11b4061
--- /dev/null
+++ b/lib/rdf/literal/datatype/registry/protocol.ex
@@ -0,0 +1,5 @@
+import ProtocolEx
+
+defprotocol_ex RDF.Literal.Datatype.Registry.Registration do
+  def datatype(id), do: nil
+end
diff --git a/lib/rdf/literal/datatypes/lang_string.ex b/lib/rdf/literal/datatypes/lang_string.ex
index 6759ca8..8d601b2 100644
--- a/lib/rdf/literal/datatypes/lang_string.ex
+++ b/lib/rdf/literal/datatypes/lang_string.ex
@@ -7,7 +7,8 @@ defmodule RDF.LangString do
 
   use RDF.Literal.Datatype,
       name: "langString",
-      id: RDF.Utils.Bootstrapping.rdf_iri("langString")
+      id: RDF.Utils.Bootstrapping.rdf_iri("langString"),
+      register: false # core datatypes don't need to be registered
 
   alias RDF.Literal.Datatype
   alias RDF.Literal
diff --git a/lib/rdf/xsd/datatypes/any_uri.ex b/lib/rdf/xsd/datatypes/any_uri.ex
index d1e15ff..3943cb0 100644
--- a/lib/rdf/xsd/datatypes/any_uri.ex
+++ b/lib/rdf/xsd/datatypes/any_uri.ex
@@ -11,7 +11,8 @@ defmodule RDF.XSD.AnyURI do
 
   use RDF.XSD.Datatype.Primitive,
     name: "anyURI",
-    id: RDF.Utils.Bootstrapping.xsd_iri("anyURI")
+    id: RDF.Utils.Bootstrapping.xsd_iri("anyURI"),
+    register: false # core datatypes don't need to be registered
 
   @impl RDF.XSD.Datatype
   @spec lexical_mapping(String.t(), Keyword.t()) :: valid_value
diff --git a/lib/rdf/xsd/datatypes/boolean.ex b/lib/rdf/xsd/datatypes/boolean.ex
index 6e012f1..740e6c3 100644
--- a/lib/rdf/xsd/datatypes/boolean.ex
+++ b/lib/rdf/xsd/datatypes/boolean.ex
@@ -8,7 +8,8 @@ defmodule RDF.XSD.Boolean do
 
   use RDF.XSD.Datatype.Primitive,
     name: "boolean",
-    id: RDF.Utils.Bootstrapping.xsd_iri("boolean")
+    id: RDF.Utils.Bootstrapping.xsd_iri("boolean"),
+    register: false # core datatypes don't need to be registered
 
   @impl RDF.XSD.Datatype
   def lexical_mapping(lexical, _) do
diff --git a/lib/rdf/xsd/datatypes/byte.ex b/lib/rdf/xsd/datatypes/byte.ex
index b1e4a8d..e63a46e 100644
--- a/lib/rdf/xsd/datatypes/byte.ex
+++ b/lib/rdf/xsd/datatypes/byte.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.Byte do
   use RDF.XSD.Datatype.Restriction,
     name: "byte",
     id: RDF.Utils.Bootstrapping.xsd_iri("byte"),
-    base: RDF.XSD.Short
+    base: RDF.XSD.Short,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, -128
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 127
diff --git a/lib/rdf/xsd/datatypes/date.ex b/lib/rdf/xsd/datatypes/date.ex
index 95b94d1..803931b 100644
--- a/lib/rdf/xsd/datatypes/date.ex
+++ b/lib/rdf/xsd/datatypes/date.ex
@@ -11,7 +11,8 @@ defmodule RDF.XSD.Date do
 
   use RDF.XSD.Datatype.Primitive,
     name: "date",
-    id: RDF.Utils.Bootstrapping.xsd_iri("date")
+    id: RDF.Utils.Bootstrapping.xsd_iri("date"),
+    register: false # core datatypes don't need to be registered
 
 
   # TODO: Are GMT/UTC actually allowed? Maybe because it is supported by Elixir's Datetime ...
diff --git a/lib/rdf/xsd/datatypes/date_time.ex b/lib/rdf/xsd/datatypes/date_time.ex
index e49f501..efe2a17 100644
--- a/lib/rdf/xsd/datatypes/date_time.ex
+++ b/lib/rdf/xsd/datatypes/date_time.ex
@@ -7,7 +7,8 @@ defmodule RDF.XSD.DateTime do
 
   use RDF.XSD.Datatype.Primitive,
     name: "dateTime",
-    id: RDF.Utils.Bootstrapping.xsd_iri("dateTime")
+    id: RDF.Utils.Bootstrapping.xsd_iri("dateTime"),
+    register: false # core datatypes don't need to be registered
 
   @impl RDF.XSD.Datatype
   def lexical_mapping(lexical, opts) do
diff --git a/lib/rdf/xsd/datatypes/decimal.ex b/lib/rdf/xsd/datatypes/decimal.ex
index 835ec07..60c1b5e 100644
--- a/lib/rdf/xsd/datatypes/decimal.ex
+++ b/lib/rdf/xsd/datatypes/decimal.ex
@@ -7,7 +7,8 @@ defmodule RDF.XSD.Decimal do
 
   use RDF.XSD.Datatype.Primitive,
     name: "decimal",
-    id: RDF.Utils.Bootstrapping.xsd_iri("decimal")
+    id: RDF.Utils.Bootstrapping.xsd_iri("decimal"),
+    register: false # core datatypes don't need to be registered
 
   alias Elixir.Decimal, as: D
 
diff --git a/lib/rdf/xsd/datatypes/double.ex b/lib/rdf/xsd/datatypes/double.ex
index b7861c7..f54f896 100644
--- a/lib/rdf/xsd/datatypes/double.ex
+++ b/lib/rdf/xsd/datatypes/double.ex
@@ -8,7 +8,8 @@ defmodule RDF.XSD.Double do
 
   use RDF.XSD.Datatype.Primitive,
     name: "double",
-    id: RDF.Utils.Bootstrapping.xsd_iri("double")
+    id: RDF.Utils.Bootstrapping.xsd_iri("double"),
+    register: false # core datatypes don't need to be registered
 
   @special_values ~W[positive_infinity negative_infinity nan]a
 
diff --git a/lib/rdf/xsd/datatypes/float.ex b/lib/rdf/xsd/datatypes/float.ex
index 6e3108a..7c0fcc0 100644
--- a/lib/rdf/xsd/datatypes/float.ex
+++ b/lib/rdf/xsd/datatypes/float.ex
@@ -9,5 +9,6 @@ defmodule RDF.XSD.Float do
   use RDF.XSD.Datatype.Restriction,
     name: "float",
     id: RDF.Utils.Bootstrapping.xsd_iri("float"),
-    base: RDF.XSD.Double
+    base: RDF.XSD.Double,
+    register: false # core datatypes don't need to be registered
 end
diff --git a/lib/rdf/xsd/datatypes/int.ex b/lib/rdf/xsd/datatypes/int.ex
index 1844084..6f3fbb5 100644
--- a/lib/rdf/xsd/datatypes/int.ex
+++ b/lib/rdf/xsd/datatypes/int.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.Int do
   use RDF.XSD.Datatype.Restriction,
     name: "int",
     id: RDF.Utils.Bootstrapping.xsd_iri("int"),
-    base: RDF.XSD.Long
+    base: RDF.XSD.Long,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, -2_147_483_648
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 2_147_483_647
diff --git a/lib/rdf/xsd/datatypes/integer.ex b/lib/rdf/xsd/datatypes/integer.ex
index 05e8135..4078bad 100644
--- a/lib/rdf/xsd/datatypes/integer.ex
+++ b/lib/rdf/xsd/datatypes/integer.ex
@@ -10,7 +10,8 @@ defmodule RDF.XSD.Integer do
 
   use RDF.XSD.Datatype.Primitive,
     name: "integer",
-    id: RDF.Utils.Bootstrapping.xsd_iri("integer")
+    id: RDF.Utils.Bootstrapping.xsd_iri("integer"),
+    register: false # core datatypes don't need to be registered
 
   def_applicable_facet RDF.XSD.Facets.MinInclusive
   def_applicable_facet RDF.XSD.Facets.MaxInclusive
diff --git a/lib/rdf/xsd/datatypes/long.ex b/lib/rdf/xsd/datatypes/long.ex
index fc6617b..f3094fa 100644
--- a/lib/rdf/xsd/datatypes/long.ex
+++ b/lib/rdf/xsd/datatypes/long.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.Long do
   use RDF.XSD.Datatype.Restriction,
     name: "long",
     id: RDF.Utils.Bootstrapping.xsd_iri("long"),
-    base: RDF.XSD.Integer
+    base: RDF.XSD.Integer,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, -9_223_372_036_854_775_808
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 9_223_372_036_854_775_807
diff --git a/lib/rdf/xsd/datatypes/negative_integer.ex b/lib/rdf/xsd/datatypes/negative_integer.ex
index 4bb0c4f..2f934a7 100644
--- a/lib/rdf/xsd/datatypes/negative_integer.ex
+++ b/lib/rdf/xsd/datatypes/negative_integer.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.NegativeInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "negativeInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("negativeInteger"),
-    base: RDF.XSD.NonPositiveInteger
+    base: RDF.XSD.NonPositiveInteger,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, -1
 end
diff --git a/lib/rdf/xsd/datatypes/non_negative_integer.ex b/lib/rdf/xsd/datatypes/non_negative_integer.ex
index 3129cdf..547ddca 100644
--- a/lib/rdf/xsd/datatypes/non_negative_integer.ex
+++ b/lib/rdf/xsd/datatypes/non_negative_integer.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.NonNegativeInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "nonNegativeInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("nonNegativeInteger"),
-    base: RDF.XSD.Integer
+    base: RDF.XSD.Integer,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
 end
diff --git a/lib/rdf/xsd/datatypes/non_positive_integer.ex b/lib/rdf/xsd/datatypes/non_positive_integer.ex
index 5048529..9206eb3 100644
--- a/lib/rdf/xsd/datatypes/non_positive_integer.ex
+++ b/lib/rdf/xsd/datatypes/non_positive_integer.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.NonPositiveInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "nonPositiveInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("nonPositiveInteger"),
-    base: RDF.XSD.Integer
+    base: RDF.XSD.Integer,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 0
 end
diff --git a/lib/rdf/xsd/datatypes/positive_integer.ex b/lib/rdf/xsd/datatypes/positive_integer.ex
index 1b8117f..dcb5c18 100644
--- a/lib/rdf/xsd/datatypes/positive_integer.ex
+++ b/lib/rdf/xsd/datatypes/positive_integer.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.PositiveInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "positiveInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("positiveInteger"),
-    base: RDF.XSD.NonNegativeInteger
+    base: RDF.XSD.NonNegativeInteger,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 1
 end
diff --git a/lib/rdf/xsd/datatypes/short.ex b/lib/rdf/xsd/datatypes/short.ex
index 96df409..1ea8a15 100644
--- a/lib/rdf/xsd/datatypes/short.ex
+++ b/lib/rdf/xsd/datatypes/short.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.Short do
   use RDF.XSD.Datatype.Restriction,
     name: "short",
     id: RDF.Utils.Bootstrapping.xsd_iri("short"),
-    base: RDF.XSD.Int
+    base: RDF.XSD.Int,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, -32768
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 32767
diff --git a/lib/rdf/xsd/datatypes/string.ex b/lib/rdf/xsd/datatypes/string.ex
index 023ff40..1cc9bfc 100644
--- a/lib/rdf/xsd/datatypes/string.ex
+++ b/lib/rdf/xsd/datatypes/string.ex
@@ -7,7 +7,8 @@ defmodule RDF.XSD.String do
 
   use RDF.XSD.Datatype.Primitive,
     name: "string",
-    id: RDF.Utils.Bootstrapping.xsd_iri("string")
+    id: RDF.Utils.Bootstrapping.xsd_iri("string"),
+    register: false # core datatypes don't need to be registered
 
   @impl RDF.XSD.Datatype
   @spec lexical_mapping(String.t(), Keyword.t()) :: valid_value
diff --git a/lib/rdf/xsd/datatypes/time.ex b/lib/rdf/xsd/datatypes/time.ex
index 78d4ecc..a85ae3d 100644
--- a/lib/rdf/xsd/datatypes/time.ex
+++ b/lib/rdf/xsd/datatypes/time.ex
@@ -7,7 +7,8 @@ defmodule RDF.XSD.Time do
 
   use RDF.XSD.Datatype.Primitive,
     name: "time",
-    id: RDF.Utils.Bootstrapping.xsd_iri("time")
+    id: RDF.Utils.Bootstrapping.xsd_iri("time"),
+    register: false # core datatypes don't need to be registered
 
   # TODO: Are GMT/UTC actually allowed? Maybe because it is supported by Elixir's Datetime ...
   @grammar ~r/\A(\d{2}:\d{2}:\d{2}(?:\.\d+)?)((?:[\+\-]\d{2}:\d{2})|UTC|GMT|Z)?\Z/
diff --git a/lib/rdf/xsd/datatypes/unsigned_byte.ex b/lib/rdf/xsd/datatypes/unsigned_byte.ex
index 9742bd1..ece87f4 100644
--- a/lib/rdf/xsd/datatypes/unsigned_byte.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_byte.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.UnsignedByte do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedByte",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedByte"),
-    base: RDF.XSD.UnsignedShort
+    base: RDF.XSD.UnsignedShort,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 255
diff --git a/lib/rdf/xsd/datatypes/unsigned_int.ex b/lib/rdf/xsd/datatypes/unsigned_int.ex
index 5864444..63d1ad1 100644
--- a/lib/rdf/xsd/datatypes/unsigned_int.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_int.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.UnsignedInt do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedInt",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedInt"),
-    base: RDF.XSD.UnsignedLong
+    base: RDF.XSD.UnsignedLong,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 4_294_967_295
diff --git a/lib/rdf/xsd/datatypes/unsigned_long.ex b/lib/rdf/xsd/datatypes/unsigned_long.ex
index f7d0d8c..9aed230 100644
--- a/lib/rdf/xsd/datatypes/unsigned_long.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_long.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.UnsignedLong do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedLong",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedLong"),
-    base: RDF.XSD.NonNegativeInteger
+    base: RDF.XSD.NonNegativeInteger,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 18_446_744_073_709_551_615
diff --git a/lib/rdf/xsd/datatypes/unsigned_short.ex b/lib/rdf/xsd/datatypes/unsigned_short.ex
index baa2d72..cf8e84f 100644
--- a/lib/rdf/xsd/datatypes/unsigned_short.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_short.ex
@@ -2,7 +2,8 @@ defmodule RDF.XSD.UnsignedShort do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedShort",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedShort"),
-    base: RDF.XSD.UnsignedInt
+    base: RDF.XSD.UnsignedInt,
+    register: false # core datatypes don't need to be registered
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 65535
diff --git a/mix.exs b/mix.exs
index c8f5529..9e0d260 100644
--- a/mix.exs
+++ b/mix.exs
@@ -14,6 +14,7 @@ defmodule RDF.Mixfile do
       start_permanent: Mix.env == :prod,
       deps: deps(),
       elixirc_paths: elixirc_paths(Mix.env()),
+      compilers: Mix.compilers ++ [:protocol_ex],
 
       # Dialyzer
       dialyzer: dialyzer(),
@@ -68,6 +69,7 @@ defmodule RDF.Mixfile do
   defp deps do
     [
       {:decimal, "~> 1.5"},
+      {:protocol_ex, "~> 0.4"},
 
       {:credo, "~> 1.3",           only: [:dev, :test], runtime: false},
       {:dialyxir, "~> 1.0.0-rc.7", only: :dev, runtime: false},
diff --git a/mix.lock b/mix.lock
index be0ba32..d56712b 100644
--- a/mix.lock
+++ b/mix.lock
@@ -20,6 +20,7 @@
   "mimerl": {:hex, :mimerl, "1.2.0", "67e2d3f571088d5cfd3e550c383094b47159f3eee8ffa08e64106cdf5e981be3", [:rebar3], [], "hexpm", "f278585650aa581986264638ebf698f8bb19df297f66ad91b18910dfc6e19323"},
   "nimble_parsec": {:hex, :nimble_parsec, "0.5.3", "def21c10a9ed70ce22754fdeea0810dafd53c2db3219a0cd54cf5526377af1c6", [:mix], [], "hexpm", "589b5af56f4afca65217a1f3eb3fee7e79b09c40c742fddc1c312b3ac0b3399f"},
   "parse_trans": {:hex, :parse_trans, "3.3.0", "09765507a3c7590a784615cfd421d101aec25098d50b89d7aa1d66646bc571c1", [:rebar3], [], "hexpm", "17ef63abde837ad30680ea7f857dd9e7ced9476cdd7b0394432af4bfc241b960"},
+  "protocol_ex": {:hex, :protocol_ex, "0.4.3", "4acbe35da85109dc40315c1139bb7a65ebc7fc102d384cd8b3038384fbb9b282", [:mix], [], "hexpm", "6ca5ddb3505c9c86f17cd3f19838b34bf89966ae17078f79f81983b6a4391fe9"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.5", "6eaf7ad16cb568bb01753dbbd7a95ff8b91c7979482b95f38443fe2c8852a79b", [:make, :mix, :rebar3], [], "hexpm", "13104d7897e38ed7f044c4de953a6c28597d1c952075eb2e328bc6d6f2bfc496"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.4.1", "d869e4c68901dd9531385bb0c8c40444ebf624e60b6962d95952775cac5e90cd", [:rebar3], [], "hexpm", "1d1848c40487cdb0b30e8ed975e34e025860c02e419cb615d255849f3427439d"},
 }
diff --git a/test/support/test_datatypes.ex b/test/support/test_datatypes.ex
new file mode 100644
index 0000000..b21802c
--- /dev/null
+++ b/test/support/test_datatypes.ex
@@ -0,0 +1,10 @@
+defmodule RDF.TestDatatypes do
+  defmodule Age do
+    use RDF.XSD.Datatype.Restriction,
+        name: "age",
+        id: "http://example.com/Age",
+        base: RDF.XSD.PositiveInteger
+
+    def_facet_constraint RDF.XSD.Facets.MaxInclusive, 150
+  end
+end
diff --git a/test/unit/literal/datatype/registry_test.exs b/test/unit/literal/datatype/registry_test.exs
index 6ad93f8..0e225d7 100644
--- a/test/unit/literal/datatype/registry_test.exs
+++ b/test/unit/literal/datatype/registry_test.exs
@@ -1,6 +1,7 @@
 defmodule RDF.Literal.Datatype.RegistryTest do
-  use ExUnit.Case
+  use RDF.Test.Case
 
+  alias RDF.TestDatatypes.Age
   alias RDF.Literal.Datatype
   alias RDF.NS
 
@@ -36,20 +37,40 @@ defmodule RDF.Literal.Datatype.RegistryTest do
 
 
   describe "get/1" do
-    test "IRIs of supported datatypes from the XSD namespace" do
-      Enum.each(@supported_xsd_datatypes, fn xsd_datatype_iri ->
-        assert xsd_datatype = Datatype.Registry.get(xsd_datatype_iri)
-        assert xsd_datatype == Datatype.Registry.get(to_string(xsd_datatype_iri))
-        assert RDF.iri(xsd_datatype.id) == xsd_datatype_iri
-
+    test "core datatypes" do
+      Enum.each(Datatype.Registry.core_datatypes(), fn datatype ->
+        assert datatype == Datatype.Registry.get(datatype.id)
+        assert datatype == Datatype.Registry.get(to_string(datatype.id))
       end)
     end
 
-    test "IRIs of unsupported datatypes from the XSD namespace" do
+    test "supported datatypes from the XSD namespace" do
+      Enum.each(@supported_xsd_datatypes, fn xsd_datatype_iri ->
+        assert xsd_datatype = Datatype.Registry.get(xsd_datatype_iri)
+        assert xsd_datatype.id == xsd_datatype_iri
+      end)
+    end
+
+    test "unsupported datatypes from the XSD namespace" do
       Enum.each(@unsupported_xsd_datatypes, fn xsd_datatype_iri ->
         refute Datatype.Registry.get(xsd_datatype_iri)
         refute Datatype.Registry.get(to_string(xsd_datatype_iri))
       end)
     end
+
+    test "with IRI of custom datatype" do
+      assert Age == Datatype.Registry.get(Age.id)
+    end
+
+    test "with namespace terms" do
+      assert Age == Datatype.Registry.get(EX.Age)
+    end
+  end
+
+  test "core datatypes are handled differently and should not be registered (for performance reasons)" do
+    Enum.each(Datatype.Registry.core_datatypes(), fn datatype ->
+      refute Datatype.Registry.Registration.datatype(datatype.id)
+      refute Datatype.Registry.Registration.datatype(to_string(datatype.id))
+    end)
   end
 end
diff --git a/test/unit/literal_test.exs b/test/unit/literal_test.exs
index d20c9fe..b04085e 100644
--- a/test/unit/literal_test.exs
+++ b/test/unit/literal_test.exs
@@ -1,7 +1,6 @@
 defmodule RDF.LiteralTest do
-  use ExUnit.Case
+  use RDF.Test.Case
 
-  import RDF.Sigils
   import RDF.TestLiterals
 
   alias RDF.{Literal, XSD, LangString}
@@ -31,13 +30,18 @@ defmodule RDF.LiteralTest do
       end
     end
 
-    test "with typed literals" do
-      Enum.each Datatype.Registry.datatypes(), fn datatype ->
+    test "with core datatype literals" do
+      Enum.each Datatype.Registry.core_datatypes(), fn datatype ->
         datatype_literal = datatype.new("foo").literal
         assert %Literal{literal: ^datatype_literal} = Literal.new(datatype_literal)
       end
     end
 
+    test "with custom datatype literals" do
+      datatype_literal = RDF.TestDatatypes.Age.new(42).literal
+      assert %Literal{literal: typed_literal} = Literal.new(datatype_literal)
+    end
+
     test "when options without datatype given" do
       assert Literal.new(true, []) == XSD.Boolean.new(true)
       assert Literal.new(42, [])   == XSD.Integer.new(42)
@@ -80,6 +84,10 @@ defmodule RDF.LiteralTest do
       assert Literal.new("foo", datatype: NS.XSD.string) == XSD.String.new("foo")
     end
 
+    test "registered custom datatype" do
+      assert Literal.new(42, datatype: EX.Age) == RDF.TestDatatypes.Age.new(42)
+    end
+
     test "unmapped/unknown datatype" do
       assert Literal.new("custom typed value", datatype: "http://example/dt") ==
                Generic.new("custom typed value", datatype: "http://example/dt")