diff --git a/lib/rdf/graph_builder.ex b/lib/rdf/graph_builder.ex
index a21f1a6..fc3bd21 100644
--- a/lib/rdf/graph_builder.ex
+++ b/lib/rdf/graph_builder.ex
@@ -1,5 +1,5 @@
 defmodule RDF.Graph.Builder do
-  alias RDF.{Description, Graph, Dataset, PrefixMap}
+  alias RDF.{Description, Graph, Dataset, PrefixMap, IRI}
 
   defmodule Error do
     defexception [:message]
@@ -16,8 +16,11 @@ defmodule RDF.Graph.Builder do
 
   def build({:__block__, _, block}, opts) do
     {declarations, data} = Enum.split_with(block, &declaration?/1)
-    {prefixes, declarations} = extract_prefixes(declarations)
     {base, declarations} = extract_base(declarations)
+    base_string = base_string(base)
+    data = resolve_relative_iris(data, base_string)
+    declarations = resolve_relative_iris(declarations, base_string)
+    {prefixes, declarations} = extract_prefixes(declarations)
 
     quote do
       alias RDF.XSD
@@ -28,7 +31,12 @@ defmodule RDF.Graph.Builder do
 
       unquote(declarations)
 
-      RDF.Graph.Builder.do_build(unquote(data), unquote(opts), unquote(prefixes), unquote(base))
+      RDF.Graph.Builder.do_build(
+        unquote(data),
+        unquote(opts),
+        unquote(prefixes),
+        unquote(base_string)
+      )
     end
   end
 
@@ -60,6 +68,31 @@ defmodule RDF.Graph.Builder do
     end)
   end
 
+  defp base_string(nil), do: nil
+  defp base_string(base) when is_binary(base), do: base
+  defp base_string(base) when is_atom(base), do: apply(base, :__base_iri__, [])
+  defp base_string({:sigil_I, _, [{_, _, [base]}, _]}), do: base
+
+  defp base_string(_) do
+    raise Error,
+      message: "invalid @base expression; only literal values are allowed as @base value"
+  end
+
+  defp resolve_relative_iris(ast, base) do
+    Macro.prewalk(ast, fn
+      {:sigil_I, meta_outer, [{:<<>>, meta_inner, [iri]}, list]} = sigil ->
+        if IRI.absolute?(iri) do
+          sigil
+        else
+          absolute = iri |> IRI.absolute(base) |> IRI.to_string()
+          {:sigil_I, meta_outer, [{:<<>>, meta_inner, [absolute]}, list]}
+        end
+
+      other ->
+        other
+    end)
+  end
+
   defp extract_base(declarations) do
     {base, declarations} =
       Enum.reduce(declarations, {nil, []}, fn
diff --git a/test/unit/graph_builder_test.exs b/test/unit/graph_builder_test.exs
index aa75fc8..c299580 100644
--- a/test/unit/graph_builder_test.exs
+++ b/test/unit/graph_builder_test.exs
@@ -12,7 +12,7 @@ defmodule RDF.Graph.BuilderTest do
   defmodule TestNS do
     use RDF.Vocabulary.Namespace
     defvocab EX, base_iri: "http://example.com/", terms: [], strict: false
-    defvocab Custom, base_iri: "http://custom.com/foo#", terms: [], strict: false
+    defvocab Custom, base_iri: "http://custom.com/foo/", terms: [], strict: false
     defvocab ImportTest, base_iri: "http://import.com/bar#", terms: [:foo, :Bar]
   end
 
@@ -410,6 +410,8 @@ defmodule RDF.Graph.BuilderTest do
 
   describe "@base" do
     test "with vocabulary namespace" do
+      import RDF.Sigils
+
       # we're wrapping this in a function to isolate the alias
       graph =
         (fn ->
@@ -418,12 +420,17 @@ defmodule RDF.Graph.BuilderTest do
              # @base TestNS.Custom
              @base RDF.Graph.BuilderTest.TestNS.Custom
 
-             Custom.S |> Custom.p(Custom.O)
+             ~I<S> |> Custom.p(~I<O>)
+             {~I<foo>, ~I<bar>, ~I<baz>}
            end
          end).()
 
       assert graph ==
-               RDF.graph(TestNS.Custom.S |> TestNS.Custom.p(TestNS.Custom.O),
+               RDF.graph(
+                 [
+                   TestNS.Custom.S |> TestNS.Custom.p(TestNS.Custom.O),
+                   TestNS.Custom.foo() |> TestNS.Custom.bar(TestNS.Custom.baz())
+                 ],
                  base_iri: TestNS.Custom
                )
     end
@@ -433,10 +440,19 @@ defmodule RDF.Graph.BuilderTest do
         RDF.Graph.build do
           @base ~I<http://example.com/base>
 
-          EX.S |> EX.p(EX.O)
+          ~I<#S> |> EX.p(~I<#O>)
+          {~I<#foo>, ~I<#bar>, ~I<#baz>}
         end
 
-      assert graph == RDF.graph(EX.S |> EX.p(EX.O), base_iri: "http://example.com/base")
+      assert graph ==
+               RDF.graph(
+                 [
+                   ~I<http://example.com/base#S> |> EX.p(~I<http://example.com/base#O>),
+                   {~I<http://example.com/base#foo>, ~I<http://example.com/base#bar>,
+                    ~I<http://example.com/base#baz>}
+                 ],
+                 base_iri: "http://example.com/base"
+               )
     end
 
     test "with URI as string" do
@@ -444,22 +460,19 @@ defmodule RDF.Graph.BuilderTest do
         RDF.Graph.build do
           @base "http://example.com/base"
 
-          EX.S |> EX.p(EX.O)
+          ~I<#S> |> EX.p(~I<#O>)
+          {~I<#foo>, ~I<#bar>, ~I<#baz>}
         end
 
-      assert graph == RDF.graph(EX.S |> EX.p(EX.O), base_iri: "http://example.com/base")
-    end
-
-    test "with URI from variable" do
-      graph =
-        RDF.Graph.build do
-          foo = "http://example.com/base"
-          @base foo
-
-          EX.S |> EX.p(EX.O)
-        end
-
-      assert graph == RDF.graph(EX.S |> EX.p(EX.O), base_iri: "http://example.com/base")
+      assert graph ==
+               RDF.graph(
+                 [
+                   ~I<http://example.com/base#S> |> EX.p(~I<http://example.com/base#O>),
+                   {~I<http://example.com/base#foo>, ~I<http://example.com/base#bar>,
+                    ~I<http://example.com/base#baz>}
+                 ],
+                 base_iri: "http://example.com/base"
+               )
     end
 
     test "conflict with base_iri opt" do
@@ -467,10 +480,13 @@ defmodule RDF.Graph.BuilderTest do
         RDF.Graph.build base_iri: "http://example.com/old" do
           @base "http://example.com/base"
 
-          EX.S |> EX.p(EX.O)
+          ~I<#S> |> EX.p(~I<#O>)
         end
 
-      assert graph == RDF.graph(EX.S |> EX.p(EX.O), base_iri: "http://example.com/base")
+      assert graph ==
+               RDF.graph(~I<http://example.com/base#S> |> EX.p(~I<http://example.com/base#O>),
+                 base_iri: "http://example.com/base"
+               )
     end
   end