--- a/testing/web-platform/tests/tools/webdriver/webdriver/client.py
+++ b/testing/web-platform/tests/tools/webdriver/webdriver/client.py
@@ -146,28 +146,30 @@ class ActionSequence(object):
         }
         if duration is not None:
             action["duration"] = duration
         if origin is not None:
             action["origin"] = origin if isinstance(origin, basestring) else origin.json()
         self._actions.append(action)
         return self
 
-    def pointer_up(self, button):
+    def pointer_up(self, button=0):
         """Queue a pointerUp action for `button`.
 
         :param button: Pointer button to perform action with.
+                       Default: 0, which represents main device button.
         """
         self._pointer_action("pointerUp", button)
         return self
 
-    def pointer_down(self, button):
+    def pointer_down(self, button=0):
         """Queue a pointerDown action for `button`.
 
         :param button: Pointer button to perform action with.
+                       Default: 0, which represents main device button.
         """
         self._pointer_action("pointerDown", button)
         return self
 
     def click(self, element=None, button=0):
         """Queue a click with the specified button.
 
         If an element is given, move the pointer to that element first,