diff --git a/sphinx/application.py b/sphinx/application.py
index 4d861a69a..af10bb7e2 100644
--- a/sphinx/application.py
+++ b/sphinx/application.py
@@ -18,7 +18,8 @@ from os import path
 from cStringIO import StringIO
 
 from docutils import nodes
-from docutils.parsers.rst import Directive, directives, roles
+from docutils.parsers.rst import Directive, convert_directive_function, \
+     directives, roles
 
 import sphinx
 from sphinx import package_dir, locale
@@ -341,9 +342,9 @@ class Sphinx(object):
             return obj
         else:
             obj.content = content
-            obj.arguments = arguments
+            obj.arguments = arguments or (0, 0, False)
             obj.options = options
-            return obj
+            return convert_directive_function(obj)
 
     def add_directive(self, name, obj, content=None, arguments=None, **options):
         directives.register_directive(
diff --git a/sphinx/domains/__init__.py b/sphinx/domains/__init__.py
index 563fd2aa0..0ec0622fa 100644
--- a/sphinx/domains/__init__.py
+++ b/sphinx/domains/__init__.py
@@ -112,7 +112,6 @@ class Domain(object):
         if name not in self.directives:
             return None
         fullname = '%s:%s' % (self.name, name)
-        # XXX what about function-style directives?
         BaseDirective = self.directives[name]
         class DirectiveAdapter(BaseDirective):
             def run(self):
diff --git a/tests/root/conf.py b/tests/root/conf.py
index d268ae3a5..dbb2bca7e 100644
--- a/tests/root/conf.py
+++ b/tests/root/conf.py
@@ -58,7 +58,12 @@ autosummary_generate = ['autosummary']
 # modify tags from conf.py
 tags.add('confpytag')
 
+
+# -- extension API
+
+from docutils import nodes
 from sphinx import addnodes
+from sphinx.util.compat import Directive
 
 def userdesc_parse(env, sig, signode):
     x, y = sig.split(':')
@@ -67,7 +72,18 @@ def userdesc_parse(env, sig, signode):
     signode[-1] += addnodes.desc_parameter(y, y)
     return x
 
+def functional_directive(name, arguments, options, content, lineno,
+                         content_offset, block_text, state, state_machine):
+    return [nodes.strong(text='from function: %s' % options['opt'])]
+
+class ClassDirective(Directive):
+    option_spec = {'opt': lambda x: x}
+    def run(self):
+        return [nodes.strong(text='from class: %s' % self.options['opt'])]
+
 def setup(app):
     app.add_config_value('value_from_conf_py', 42, False)
+    app.add_directive('funcdir', functional_directive, opt=lambda x: x)
+    app.add_directive('clsdir', ClassDirective)
     app.add_description_unit('userdesc', 'userdescrole', '%s (userdesc)',
                              userdesc_parse)
diff --git a/tests/root/contents.txt b/tests/root/contents.txt
index e1468ad04..2d7ba8fb0 100644
--- a/tests/root/contents.txt
+++ b/tests/root/contents.txt
@@ -11,6 +11,7 @@ Contents:
    :maxdepth: 2
    :numbered:
 
+   extapi
    images
    subdir/images
    subdir/includes
diff --git a/tests/root/extapi.txt b/tests/root/extapi.txt
new file mode 100644
index 000000000..4728e3de1
--- /dev/null
+++ b/tests/root/extapi.txt
@@ -0,0 +1,10 @@
+Extension API tests
+===================
+
+Testing directives:
+
+.. funcdir::
+   :opt: Foo
+
+.. clsdir::
+   :opt: Bar
diff --git a/tests/test_build_html.py b/tests/test_build_html.py
index 7dfbef5b6..dd89ff2e0 100644
--- a/tests/test_build_html.py
+++ b/tests/test_build_html.py
@@ -66,6 +66,10 @@ HTML_XPATH = {
         ".//dt[@id='test_autodoc.function']/em": r'\*\*kwds',
         ".//dd": r'Return spam\.',
     },
+    'extapi.html': {
+        ".//strong": 'from function: Foo',
+        ".//strong": 'from class: Bar',
+    },
     'markup.html': {
         ".//title": 'set by title directive',
         ".//p/em": 'Section author: Georg Brandl',