diff --git a/aiohttp/helpers.py b/aiohttp/helpers.py
index be03975a145..a88771af797 100644
--- a/aiohttp/helpers.py
+++ b/aiohttp/helpers.py
@@ -460,7 +460,7 @@ class Timeout:
     ...         await r.text()
 
 
-    :param timeout: timeout value in seconds
+    :param timeout: timeout value in seconds or None to disable timeout logic
     :param loop: asyncio compatible event loop
     """
     def __init__(self, timeout, *, loop=None):
@@ -477,8 +477,9 @@ def __enter__(self):
         if self._task is None:
             raise RuntimeError('Timeout context manager should be used '
                                'inside a task')
-        self._cancel_handler = self._loop.call_later(
-            self._timeout, self._cancel_task)
+        if self._timeout is not None:
+            self._cancel_handler = self._loop.call_later(
+                self._timeout, self._cancel_task)
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
@@ -486,8 +487,9 @@ def __exit__(self, exc_type, exc_val, exc_tb):
             self._cancel_handler = None
             self._task = None
             raise asyncio.TimeoutError
-        self._cancel_handler.cancel()
-        self._cancel_handler = None
+        if self._timeout is not None:
+            self._cancel_handler.cancel()
+            self._cancel_handler = None
         self._task = None
 
     def _cancel_task(self):
diff --git a/tests/test_timeout.py b/tests/test_timeout.py
index 7f7b46d0c48..492da30cc22 100644
--- a/tests/test_timeout.py
+++ b/tests/test_timeout.py
@@ -50,6 +50,18 @@ def run():
     loop.run_until_complete(run())
 
 
+@pytest.mark.run_loop
+def test_timeout_disable(loop):
+    @asyncio.coroutine
+    def long_running_task():
+        yield from asyncio.sleep(0.1, loop=loop)
+        return 'done'
+
+    with Timeout(None, loop=loop):
+        resp = yield from long_running_task()
+    assert resp == 'done'
+
+
 @pytest.mark.run_loop
 def test_timeout_not_relevant_exception(loop):
     yield from asyncio.sleep(0, loop=loop)