diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5e2939..4520603 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,21 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 [Keep a CHANGELOG](http://keepachangelog.com).
 
 
+## Unreleased
+
+### Added
+
+- `RDF.PrefixMap.put/3` for adding a prefix mapping and overwrite an existing one
+ 
+### Changed
+
+- more compact Inspect form for `RDF.PrefixMap` 
+
+
+[Compare v0.9.0...HEAD](https://github.com/rdf-elixir/rdf-ex/compare/v0.9.0...HEAD)
+
+
+
 ## 0.9.0 - 2020-10-13
 
 The API of the all three RDF datastructures `RDF.Dataset`, `RDF.Graph` and 
diff --git a/lib/rdf/prefix_map.ex b/lib/rdf/prefix_map.ex
index e786a32..3ca19a1 100644
--- a/lib/rdf/prefix_map.ex
+++ b/lib/rdf/prefix_map.ex
@@ -97,6 +97,22 @@ defmodule RDF.PrefixMap do
     end
   end
 
+  @doc """
+  Adds a prefix mapping to `prefix_map` overwriting an existing mapping.
+  """
+  @spec put(t, coercible_prefix, coercible_namespace) :: t
+  def put(prefix_map, prefix, namespace)
+
+  def put(%__MODULE__{map: map}, prefix, %IRI{} = namespace) when is_atom(prefix) do
+    %__MODULE__{map: Map.put(map, prefix, namespace)}
+  end
+
+  def put(%__MODULE__{} = prefix_map, prefix, namespace) do
+    with {prefix, namespace} = normalize({prefix, namespace}) do
+      put(prefix_map, prefix, namespace)
+    end
+  end
+
   @doc """
   Merges two `RDF.PrefixMap`s.
 
diff --git a/test/unit/prefix_map_test.exs b/test/unit/prefix_map_test.exs
index 5843c4d..70400df 100644
--- a/test/unit/prefix_map_test.exs
+++ b/test/unit/prefix_map_test.exs
@@ -115,6 +115,40 @@ defmodule RDF.PrefixMapTest do
     end
   end
 
+  describe "put/3" do
+    test "when no mapping of the given prefix exists" do
+      assert PrefixMap.put(@example1, :ex2, @ex_ns2) == @example2
+    end
+
+    test "when the prefix is given as a string" do
+      assert PrefixMap.put(@example1, "ex2", @ex_ns2) == @example2
+    end
+
+    test "when the IRI namespace is given as a string" do
+      assert PrefixMap.put(@example1, :ex2, "http://example.com/bar#") == @example2
+    end
+
+    test "when the IRI namespace is given as a RDF.Vocabulary.Namespace" do
+      assert PrefixMap.put(@example1, :ex, EX) == @example4
+    end
+
+    test "when the IRI namespace is given as a RDF.Vocabulary.Namespace which is not loaded yet" do
+      assert prefix_map = PrefixMap.new() |> PrefixMap.put(:rdfs, RDF.NS.RDFS)
+      assert PrefixMap.has_prefix?(prefix_map, :rdfs)
+    end
+
+    test "when the IRI namespace is given as an atom" do
+      assert_raise RDF.Namespace.UndefinedTermError, "foo is not a term on a RDF.Namespace", fn ->
+        PrefixMap.put(@example1, :ex, :foo)
+      end
+    end
+
+    test "when a mapping of the given prefix to a different namespace already exists" do
+      assert PrefixMap.put(@example1, :ex1, "http://example.com/bar#") ==
+               PrefixMap.new(ex1: "http://example.com/bar#")
+    end
+  end
+
   describe "merge/2" do
     test "when the prefix maps are disjunctive" do
       other_prefix_map = PrefixMap.new(ex3: @ex_ns3)