diff --git a/lib/remote_storage/riak.rb b/lib/remote_storage/riak.rb
index 27ff1a3..94be481 100644
--- a/lib/remote_storage/riak.rb
+++ b/lib/remote_storage/riak.rb
@@ -95,6 +95,8 @@ module RemoteStorage
       object_exists = !object.raw_data.nil?
       existing_object_size = object_size(object)
 
+      server.halt 412 if object_exists && server.env["HTTP_IF_NONE_MATCH"] == "*"
+
       timestamp = (Time.now.to_f * 1000).to_i
       object.meta["timestamp"] = timestamp
 
diff --git a/spec/riak_spec.rb b/spec/riak_spec.rb
index f7f3b8c..f70cc72 100644
--- a/spec/riak_spec.rb
+++ b/spec/riak_spec.rb
@@ -262,6 +262,27 @@ describe "App with Riak backend" do
             last_response.body.must_equal "lorem ipsum"
           end
         end
+
+        describe "when If-None-Match header is set" do
+          before do
+            header "If-None-Match", "*"
+          end
+
+          it "fails when the document already exists" do
+            put "/jimmy/documents/archive/foo", "some awesome content"
+
+            last_response.status.must_equal 412
+
+            get "/jimmy/documents/archive/foo"
+            last_response.body.must_equal "lorem ipsum"
+          end
+
+          it "succeeds when the document does not exist" do
+            put "/jimmy/documents/archive/bar", "my little content"
+
+            last_response.status.must_equal 200
+          end
+        end
       end
 
       describe "exsting content without serializer registered for the given content-type" do