diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index e6b05b4..0000000
--- a/.travis.yml
+++ /dev/null
@@ -1,13 +0,0 @@
-language: python
-python:
-  - 3.6
-  - 3.7
-  - 3.8
-  - 3.9
-sudo: false
-
-install:
-  - pip install -r requirements_dev.txt
-
-script:
-  - python -m unittest discover -p "test*"
diff --git a/README.rst b/README.rst
index 84159e6..a55dfad 100644
--- a/README.rst
+++ b/README.rst
@@ -1,9 +1,6 @@
 pure-interface
 ==============
 
-.. image:: https://travis-ci.com/seequent/pure_interface.svg?branch=master
-    :target: https://travis-ci.com/seequent/pure_interface
-
 A Python interface library that disallows function body content on interfaces and supports adaption.
 
 Jump to the `Reference`_.
diff --git a/pure_interface.py b/pure_interface.py
index be09b8b..24dcbf7 100644
--- a/pure_interface.py
+++ b/pure_interface.py
@@ -18,7 +18,7 @@
 import weakref
 
 
-__version__ = '5.0.0'
+__version__ = '5.0.1'
 
 
 is_development = not hasattr(sys, 'frozen')
@@ -629,6 +629,8 @@ def interface_only(cls, implementation):
         if cls._pi.impl_wrapper_type is None:
             type_name = '_{}Only'.format(cls.__name__)
             attributes = {'__module__': cls.__module__}
+            if '__call__' in cls._pi.interface_names:
+                attributes['__call__'] = getattr(implementation, '__call__')
             cls._pi.impl_wrapper_type = type(type_name, (_ImplementationWrapper,), attributes)
             abc.ABCMeta.register(cls, cls._pi.impl_wrapper_type)
         return cls._pi.impl_wrapper_type(implementation, cls)
diff --git a/setup.cfg b/setup.cfg
index 80afc2d..be93c0c 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,6 +1,6 @@
 [metadata]
 name = pure_interface
-version = 5.0.0
+version = 5.0.1
 description = A Python interface library that disallows function body content on interfaces and supports adaption.
 keywords = abc interface adapt adaption mapper structural typing dataclass
 author = Tim Mitchell
diff --git a/tests/test_adaption.py b/tests/test_adaption.py
index bea4d45..b53b859 100644
--- a/tests/test_adaption.py
+++ b/tests/test_adaption.py
@@ -114,6 +114,23 @@ def speak(self, volume):
         super(SleepTalker, self).speak(volume)
 
 
+class DunderInterface(pure_interface.Interface):
+    def __call__(self, a):
+        pass
+
+    def __len__(self):
+        pass
+
+
+class DunderClass(DunderInterface, object):
+
+    def __call__(self, a):
+        super().__call__(a)
+
+    def __len__(self):
+        return 5
+
+
 class TestAdaption(unittest.TestCase):
     @classmethod
     def setUpClass(cls):
@@ -350,3 +367,16 @@ def test_adapt_interface_only(self):
             ISpeaker.adapt(talker_only)
         except:
             self.fail('adaption of interface only failed.')
+
+    def test_adapt_callable_is_callable(self):
+        dunder = DunderClass()
+        dunder_only = DunderInterface.adapt(dunder)
+        try:
+            dunder_only(1)
+        except TypeError:
+            self.fail('calling interface only failed')
+
+        try:
+            len(dunder)
+        except:
+            self.fail('len() interface only failed')
diff --git a/tox.ini b/tox.ini
index 73f966a..6ebaa44 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,6 @@ envlist = py36, py37, py38, py39
 [testenv]
 deps =
     pycontracts
-    dataclasses; python_version < 3.7
+    dataclasses; python_version < '3.7'
 commands =
     python -m unittest discover -p "test*"