diff --git a/requests/models.py b/requests/models.py
index 2193c6e5..78311491 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -462,10 +462,10 @@ class Request(object):
 
     def register_hook(self, event, hook):
         """Properly register a hook."""
-        if isinstance(hook, (list, tuple, set)):
-            self.hooks[event].extend(hook)
-        else:
+        if callable(hook):
             self.hooks[event].append(hook)
+        elif hasattr(hook, '__iter__'):
+            self.hooks[event].extend(h for h in hook if callable(h))
 
     def deregister_hook(self, event, hook):
         """Deregister a previously registered hook.
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 0f67618a..3d6f49c2 100755
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -778,6 +778,10 @@ class RequestsTestSuite(TestSetup, TestBaseMixin, unittest.TestCase):
         r = requests.models.Request(hooks={'args': hooks})
         assert_hooks_are_callable(r.hooks)
 
+        hooks.append('string that should not be registered')
+        r = requests.models.Request(hooks={'args': hooks})
+        assert_hooks_are_callable(r.hooks)
+
     def test_session_persistent_cookies(self):
 
         s = requests.session()