diff --git a/testing/web-platform/tests/tools/webdriver/webdriver/client.py b/testing/web-platform/tests/tools/webdriver/webdriver/client.py
index dc3166ab682f..b90a58c9d73d 100644
--- a/testing/web-platform/tests/tools/webdriver/webdriver/client.py
+++ b/testing/web-platform/tests/tools/webdriver/webdriver/client.py
@@ -147,18 +147,20 @@ class ActionSequence(object):
         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