diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44ac277..6bb19d6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,15 +18,21 @@ The generated namespaces are much more flexible now and compile faster.
 
 ### Changed
 
+- The `:base_iri` specified in `defvocab` can now be given in any form supported
+  by `RDF.IRI.new/1`. There are also no longer restrictions on the expression 
+  of this value. While previously the value had to be provided as a literal value,
+  now any expression returning a value accepted by `RDF.IRI.new/1` can be given 
+  (e.g. function calls, module attributes etc.).
+  The `:base_iri` also no longer has to end with a `/` or `#`.
 - Aliases on a `RDF.Vocabulary.Namespace` can now be specified directly in the 
- `:terms` list
+ `:terms` list.
 - When defining an alias for a term of vocabulary which would be invalid as an
   Elixir term, the original term is now implicitly ignored and won't any longer
   be returned by the `__terms__/0` function of a `RDF.Vocabulary.Namespace`.
 - `RDF.Data.merge/2` and `RDF.Data.equal?/2` are now commutative, i.e. structs
   which implement the `RDF.Data` protocol can be given also as the second argument
   (previously custom structs with `RDF.Data` protocol implementations always
-  had to be given as the first argument)
+  had to be given as the first argument).
 - several performance improvements
 
 
diff --git a/lib/rdf/vocabulary_namespace.ex b/lib/rdf/vocabulary_namespace.ex
index f91d484..0f71d9c 100644
--- a/lib/rdf/vocabulary_namespace.ex
+++ b/lib/rdf/vocabulary_namespace.ex
@@ -9,7 +9,7 @@ defmodule RDF.Vocabulary.Namespace do
   the `RDF.NS` module.
   """
 
-  alias RDF.{Description, Graph, Dataset, Vocabulary, Namespace}
+  alias RDF.{Description, Graph, Dataset, Vocabulary, Namespace, IRI}
 
   import RDF.Vocabulary.Namespace.{TermMapping, CaseValidation}
   import RDF.Vocabulary, only: [term_to_iri: 2, extract_terms: 2]
@@ -254,14 +254,25 @@ defmodule RDF.Vocabulary.Namespace do
     end
   end
 
-  defp normalize_base_uri(base_uri) do
-    unless is_binary(base_uri) and String.ends_with?(base_uri, ~w[/ # .]) do
-      raise RDF.Namespace.InvalidVocabBaseIRIError, "invalid base IRI: #{inspect(base_uri)}"
-    else
+  defp normalize_base_uri(%IRI{} = base_iri), do: IRI.to_string(base_iri)
+
+  defp normalize_base_uri(base_uri) when is_binary(base_uri) do
+    if IRI.valid?(base_uri) do
       base_uri
+    else
+      raise RDF.Namespace.InvalidVocabBaseIRIError, "invalid base IRI: #{inspect(base_uri)}"
     end
   end
 
+  defp normalize_base_uri(base_uri) do
+    base_uri |> IRI.new() |> normalize_base_uri()
+  rescue
+    [Namespace.UndefinedTermError, IRI.InvalidError, FunctionClauseError] ->
+      reraise RDF.Namespace.InvalidVocabBaseIRIError,
+              "invalid base IRI: #{inspect(base_uri)}",
+              __STACKTRACE__
+  end
+
   @doc false
   @spec vocabulary_namespace?(module) :: boolean
   def vocabulary_namespace?(name) do
diff --git a/test/unit/vocabulary_namespace_test.exs b/test/unit/vocabulary_namespace_test.exs
index f1612cd..624c80c 100644
--- a/test/unit/vocabulary_namespace_test.exs
+++ b/test/unit/vocabulary_namespace_test.exs
@@ -42,6 +42,15 @@ defmodule RDF.Vocabulary.NamespaceTest do
       base_iri: "http://example.com/strict#",
       terms: ~w[foo bar]
 
+    @base_iri "http://example.com/"
+    defvocab ExampleWithBaseFromModuleAttribute,
+      base_iri: @base_iri,
+      terms: ~w[foo Bar]a
+
+    defvocab ExampleWithBaseFromIRI,
+      base_iri: ~I<http://example.com/>,
+      terms: ~w[foo Bar]a
+
     defvocab ExampleFromGraph,
       base_iri: "http://example.com/from_graph#",
       data:
@@ -139,18 +148,6 @@ defmodule RDF.Vocabulary.NamespaceTest do
       end
     end
 
-    test "when the base_iri doesn't end with '/' or '#', an error is raised" do
-      assert_raise RDF.Namespace.InvalidVocabBaseIRIError, fn ->
-        defmodule NSWithInvalidBaseIRI1 do
-          use RDF.Vocabulary.Namespace
-
-          defvocab Example,
-            base_iri: "http://example.com/base_iri4",
-            terms: []
-        end
-      end
-    end
-
     test "when the base_iri isn't a valid IRI, an error is raised" do
       assert_raise RDF.Namespace.InvalidVocabBaseIRIError, fn ->
         defmodule NSWithInvalidBaseIRI2 do
@@ -957,9 +954,13 @@ defmodule RDF.Vocabulary.NamespaceTest do
   test "__base_iri__ returns the base_iri" do
     alias TestNS.ExampleFromGraph, as: HashVocab
     alias TestNS.ExampleFromNTriplesFile, as: SlashVocab
+    alias TestNS.ExampleWithBaseFromModuleAttribute, as: BaseFromModuleAttribute
+    alias TestNS.ExampleWithBaseFromIRI, as: BaseFromIRI
 
     assert HashVocab.__base_iri__() == "http://example.com/from_graph#"
     assert SlashVocab.__base_iri__() == "http://example.com/from_ntriples/"
+    assert BaseFromModuleAttribute.__base_iri__() == "http://example.com/"
+    assert BaseFromIRI.__base_iri__() == "http://example.com/"
   end
 
   test "__iris__ returns all IRIs of the vocabulary" do
@@ -1040,7 +1041,9 @@ defmodule RDF.Vocabulary.NamespaceTest do
       EXS,
       ExampleFromGraph,
       ExampleFromNTriplesFile,
-      StrictExampleFromTerms
+      StrictExampleFromTerms,
+      ExampleWithBaseFromIRI,
+      ExampleWithBaseFromModuleAttribute
     }
 
     test "undefined terms" do
@@ -1088,12 +1091,17 @@ defmodule RDF.Vocabulary.NamespaceTest do
 
       assert StrictExampleFromTerms.foo() == ~I<http://example.com/strict_from_terms#foo>
       assert RDF.iri(StrictExampleFromTerms.foo()) == ~I<http://example.com/strict_from_terms#foo>
+
+      assert ExampleWithBaseFromIRI.foo() == ~I<http://example.com/foo>
+      assert ExampleWithBaseFromModuleAttribute.foo() == ~I<http://example.com/foo>
     end
 
     test "capitalized terms" do
       assert RDF.iri(ExampleFromGraph.Bar) == ~I<http://example.com/from_graph#Bar>
       assert RDF.iri(ExampleFromNTriplesFile.Bar) == ~I<http://example.com/from_ntriples/Bar>
       assert RDF.iri(StrictExampleFromTerms.Bar) == ~I<http://example.com/strict_from_terms#Bar>
+      assert RDF.iri(ExampleWithBaseFromIRI.Bar) == ~I<http://example.com/Bar>
+      assert RDF.iri(ExampleWithBaseFromModuleAttribute.Bar) == ~I<http://example.com/Bar>
     end
 
     test "terms starting with an underscore" do