diff --git a/lib/rdf/literal/datatype/registry.ex b/lib/rdf/literal/datatype/registry.ex
index 6fb00b2..c055d8a 100644
--- a/lib/rdf/literal/datatype/registry.ex
+++ b/lib/rdf/literal/datatype/registry.ex
@@ -1,7 +1,7 @@
 defmodule RDF.Literal.Datatype.Registry do
   @moduledoc false
 
-  alias RDF.{Literal, IRI, XSD}
+  alias RDF.{Literal, IRI, XSD, Namespace}
   alias RDF.Literal.Datatype.Registry.Registration
 
   import RDF.Guards
@@ -46,15 +46,9 @@ 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) 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
+  def get(%IRI{} = id), do: id |> to_string() |> get()
+  def get(id) when maybe_ns_term(id), do: id |> Namespace.resolve_term!() |> get()
+  def get(id) when is_binary(id), do: Registration.datatype(id)
 
   defp implements_datatype_behaviour?(module) do
     module.module_info[:attributes]
diff --git a/lib/rdf/literal/datatypes/lang_string.ex b/lib/rdf/literal/datatypes/lang_string.ex
index 8d601b2..6759ca8 100644
--- a/lib/rdf/literal/datatypes/lang_string.ex
+++ b/lib/rdf/literal/datatypes/lang_string.ex
@@ -7,8 +7,7 @@ defmodule RDF.LangString do
 
   use RDF.Literal.Datatype,
       name: "langString",
-      id: RDF.Utils.Bootstrapping.rdf_iri("langString"),
-      register: false # core datatypes don't need to be registered
+      id: RDF.Utils.Bootstrapping.rdf_iri("langString")
 
   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 3943cb0..d1e15ff 100644
--- a/lib/rdf/xsd/datatypes/any_uri.ex
+++ b/lib/rdf/xsd/datatypes/any_uri.ex
@@ -11,8 +11,7 @@ defmodule RDF.XSD.AnyURI do
 
   use RDF.XSD.Datatype.Primitive,
     name: "anyURI",
-    id: RDF.Utils.Bootstrapping.xsd_iri("anyURI"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("anyURI")
 
   @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 740e6c3..6e012f1 100644
--- a/lib/rdf/xsd/datatypes/boolean.ex
+++ b/lib/rdf/xsd/datatypes/boolean.ex
@@ -8,8 +8,7 @@ defmodule RDF.XSD.Boolean do
 
   use RDF.XSD.Datatype.Primitive,
     name: "boolean",
-    id: RDF.Utils.Bootstrapping.xsd_iri("boolean"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("boolean")
 
   @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 e63a46e..b1e4a8d 100644
--- a/lib/rdf/xsd/datatypes/byte.ex
+++ b/lib/rdf/xsd/datatypes/byte.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.Byte do
   use RDF.XSD.Datatype.Restriction,
     name: "byte",
     id: RDF.Utils.Bootstrapping.xsd_iri("byte"),
-    base: RDF.XSD.Short,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Short
 
   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 803931b..95b94d1 100644
--- a/lib/rdf/xsd/datatypes/date.ex
+++ b/lib/rdf/xsd/datatypes/date.ex
@@ -11,8 +11,7 @@ defmodule RDF.XSD.Date do
 
   use RDF.XSD.Datatype.Primitive,
     name: "date",
-    id: RDF.Utils.Bootstrapping.xsd_iri("date"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("date")
 
 
   # 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 efe2a17..e49f501 100644
--- a/lib/rdf/xsd/datatypes/date_time.ex
+++ b/lib/rdf/xsd/datatypes/date_time.ex
@@ -7,8 +7,7 @@ defmodule RDF.XSD.DateTime do
 
   use RDF.XSD.Datatype.Primitive,
     name: "dateTime",
-    id: RDF.Utils.Bootstrapping.xsd_iri("dateTime"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("dateTime")
 
   @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 60c1b5e..835ec07 100644
--- a/lib/rdf/xsd/datatypes/decimal.ex
+++ b/lib/rdf/xsd/datatypes/decimal.ex
@@ -7,8 +7,7 @@ defmodule RDF.XSD.Decimal do
 
   use RDF.XSD.Datatype.Primitive,
     name: "decimal",
-    id: RDF.Utils.Bootstrapping.xsd_iri("decimal"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("decimal")
 
   alias Elixir.Decimal, as: D
 
diff --git a/lib/rdf/xsd/datatypes/double.ex b/lib/rdf/xsd/datatypes/double.ex
index f54f896..b7861c7 100644
--- a/lib/rdf/xsd/datatypes/double.ex
+++ b/lib/rdf/xsd/datatypes/double.ex
@@ -8,8 +8,7 @@ defmodule RDF.XSD.Double do
 
   use RDF.XSD.Datatype.Primitive,
     name: "double",
-    id: RDF.Utils.Bootstrapping.xsd_iri("double"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("double")
 
   @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 7c0fcc0..6e3108a 100644
--- a/lib/rdf/xsd/datatypes/float.ex
+++ b/lib/rdf/xsd/datatypes/float.ex
@@ -9,6 +9,5 @@ defmodule RDF.XSD.Float do
   use RDF.XSD.Datatype.Restriction,
     name: "float",
     id: RDF.Utils.Bootstrapping.xsd_iri("float"),
-    base: RDF.XSD.Double,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Double
 end
diff --git a/lib/rdf/xsd/datatypes/int.ex b/lib/rdf/xsd/datatypes/int.ex
index 6f3fbb5..1844084 100644
--- a/lib/rdf/xsd/datatypes/int.ex
+++ b/lib/rdf/xsd/datatypes/int.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.Int do
   use RDF.XSD.Datatype.Restriction,
     name: "int",
     id: RDF.Utils.Bootstrapping.xsd_iri("int"),
-    base: RDF.XSD.Long,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Long
 
   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 4078bad..05e8135 100644
--- a/lib/rdf/xsd/datatypes/integer.ex
+++ b/lib/rdf/xsd/datatypes/integer.ex
@@ -10,8 +10,7 @@ defmodule RDF.XSD.Integer do
 
   use RDF.XSD.Datatype.Primitive,
     name: "integer",
-    id: RDF.Utils.Bootstrapping.xsd_iri("integer"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("integer")
 
   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 f3094fa..fc6617b 100644
--- a/lib/rdf/xsd/datatypes/long.ex
+++ b/lib/rdf/xsd/datatypes/long.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.Long do
   use RDF.XSD.Datatype.Restriction,
     name: "long",
     id: RDF.Utils.Bootstrapping.xsd_iri("long"),
-    base: RDF.XSD.Integer,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Integer
 
   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 2f934a7..4bb0c4f 100644
--- a/lib/rdf/xsd/datatypes/negative_integer.ex
+++ b/lib/rdf/xsd/datatypes/negative_integer.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.NegativeInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "negativeInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("negativeInteger"),
-    base: RDF.XSD.NonPositiveInteger,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.NonPositiveInteger
 
   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 547ddca..3129cdf 100644
--- a/lib/rdf/xsd/datatypes/non_negative_integer.ex
+++ b/lib/rdf/xsd/datatypes/non_negative_integer.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.NonNegativeInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "nonNegativeInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("nonNegativeInteger"),
-    base: RDF.XSD.Integer,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Integer
 
   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 9206eb3..5048529 100644
--- a/lib/rdf/xsd/datatypes/non_positive_integer.ex
+++ b/lib/rdf/xsd/datatypes/non_positive_integer.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.NonPositiveInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "nonPositiveInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("nonPositiveInteger"),
-    base: RDF.XSD.Integer,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Integer
 
   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 dcb5c18..1b8117f 100644
--- a/lib/rdf/xsd/datatypes/positive_integer.ex
+++ b/lib/rdf/xsd/datatypes/positive_integer.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.PositiveInteger do
   use RDF.XSD.Datatype.Restriction,
     name: "positiveInteger",
     id: RDF.Utils.Bootstrapping.xsd_iri("positiveInteger"),
-    base: RDF.XSD.NonNegativeInteger,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.NonNegativeInteger
 
   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 1ea8a15..96df409 100644
--- a/lib/rdf/xsd/datatypes/short.ex
+++ b/lib/rdf/xsd/datatypes/short.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.Short do
   use RDF.XSD.Datatype.Restriction,
     name: "short",
     id: RDF.Utils.Bootstrapping.xsd_iri("short"),
-    base: RDF.XSD.Int,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.Int
 
   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 3544dd0..aeeb8f3 100644
--- a/lib/rdf/xsd/datatypes/string.ex
+++ b/lib/rdf/xsd/datatypes/string.ex
@@ -7,8 +7,7 @@ defmodule RDF.XSD.String do
 
   use RDF.XSD.Datatype.Primitive,
     name: "string",
-    id: RDF.Utils.Bootstrapping.xsd_iri("string"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("string")
 
   @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 a85ae3d..78d4ecc 100644
--- a/lib/rdf/xsd/datatypes/time.ex
+++ b/lib/rdf/xsd/datatypes/time.ex
@@ -7,8 +7,7 @@ defmodule RDF.XSD.Time do
 
   use RDF.XSD.Datatype.Primitive,
     name: "time",
-    id: RDF.Utils.Bootstrapping.xsd_iri("time"),
-    register: false # core datatypes don't need to be registered
+    id: RDF.Utils.Bootstrapping.xsd_iri("time")
 
   # 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 ece87f4..9742bd1 100644
--- a/lib/rdf/xsd/datatypes/unsigned_byte.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_byte.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.UnsignedByte do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedByte",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedByte"),
-    base: RDF.XSD.UnsignedShort,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.UnsignedShort
 
   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 63d1ad1..5864444 100644
--- a/lib/rdf/xsd/datatypes/unsigned_int.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_int.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.UnsignedInt do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedInt",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedInt"),
-    base: RDF.XSD.UnsignedLong,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.UnsignedLong
 
   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 9aed230..f7d0d8c 100644
--- a/lib/rdf/xsd/datatypes/unsigned_long.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_long.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.UnsignedLong do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedLong",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedLong"),
-    base: RDF.XSD.NonNegativeInteger,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.NonNegativeInteger
 
   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 cf8e84f..baa2d72 100644
--- a/lib/rdf/xsd/datatypes/unsigned_short.ex
+++ b/lib/rdf/xsd/datatypes/unsigned_short.ex
@@ -2,8 +2,7 @@ defmodule RDF.XSD.UnsignedShort do
   use RDF.XSD.Datatype.Restriction,
     name: "unsignedShort",
     id: RDF.Utils.Bootstrapping.xsd_iri("unsignedShort"),
-    base: RDF.XSD.UnsignedInt,
-    register: false # core datatypes don't need to be registered
+    base: RDF.XSD.UnsignedInt
 
   def_facet_constraint RDF.XSD.Facets.MinInclusive, 0
   def_facet_constraint RDF.XSD.Facets.MaxInclusive, 65535
diff --git a/test/unit/literal/datatype/registry_test.exs b/test/unit/literal/datatype/registry_test.exs
index 0e225d7..30e2345 100644
--- a/test/unit/literal/datatype/registry_test.exs
+++ b/test/unit/literal/datatype/registry_test.exs
@@ -66,11 +66,4 @@ defmodule RDF.Literal.Datatype.RegistryTest 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