diff --git a/py/selenium/webdriver/common/bidi/browsing_context.py b/py/selenium/webdriver/common/bidi/browsing_context.py
index 403e10b87d539..696a4f73bbb5f 100644
--- a/py/selenium/webdriver/common/bidi/browsing_context.py
+++ b/py/selenium/webdriver/common/bidi/browsing_context.py
@@ -20,9 +20,13 @@
 from dataclasses import dataclass
 from typing import Any
 
+from typing_extensions import Sentinel
+
 from selenium.webdriver.common.bidi.common import command_builder
 from selenium.webdriver.common.bidi.session import Session
 
+UNDEFINED = Sentinel("UNDEFINED")
+
 
 class ReadinessState:
     """Represents the stage of document loading at which a navigation command will return."""
@@ -980,30 +984,38 @@ def reload(
     def set_viewport(
         self,
         context: str | None = None,
-        viewport: dict | None = None,
-        device_pixel_ratio: float | None = None,
+        viewport: dict | None | UNDEFINED = UNDEFINED,
+        device_pixel_ratio: float | None | UNDEFINED = UNDEFINED,
         user_contexts: list[str] | None = None,
     ) -> None:
         """Modifies specific viewport characteristics on the given top-level traversable.
 
         Args:
             context: The browsing context ID.
-            viewport: The viewport parameters.
-            device_pixel_ratio: The device pixel ratio.
+            viewport: The viewport parameters - {"width": <int>, "height": <int>} (`None` resets to default).
+            device_pixel_ratio: The device pixel ratio (`None` resets to default).
             user_contexts: The user context IDs.
 
         Raises:
-            Exception: If the browsing context is not a top-level traversable.
+            Exception: If the browsing context is not a top-level traversable
+            ValueError: If neither `context` nor `user_contexts` is provided
+            ValueError: If both `context` and `user_contexts` are provided
         """
+        if context is not None and user_contexts is not None:
+            raise ValueError("Cannot specify both context and user_contexts")
+
+        if context is None and user_contexts is None:
+            raise ValueError("Must specify either context or user_contexts")
+
         params: dict[str, Any] = {}
         if context is not None:
             params["context"] = context
-        if viewport is not None:
+        elif user_contexts is not None:
+            params["userContexts"] = user_contexts
+        if viewport is not UNDEFINED:
             params["viewport"] = viewport
-        if device_pixel_ratio is not None:
+        if device_pixel_ratio is not UNDEFINED:
             params["devicePixelRatio"] = device_pixel_ratio
-        if user_contexts is not None:
-            params["userContexts"] = user_contexts
 
         self.conn.execute(command_builder("browsingContext.setViewport", params))
 
diff --git a/py/test/selenium/webdriver/common/bidi_browsing_context_tests.py b/py/test/selenium/webdriver/common/bidi_browsing_context_tests.py
index fb9941582a395..c5c9284418ba2 100644
--- a/py/test/selenium/webdriver/common/bidi_browsing_context_tests.py
+++ b/py/test/selenium/webdriver/common/bidi_browsing_context_tests.py
@@ -348,12 +348,15 @@ def test_set_viewport(driver, pages):
     context_id = driver.current_window_handle
     driver.get(pages.url("formPage.html"))
 
-    driver.browsing_context.set_viewport(context=context_id, viewport={"width": 250, "height": 300})
+    try:
+        driver.browsing_context.set_viewport(context=context_id, viewport={"width": 251, "height": 301})
 
-    viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
+        viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
 
-    assert viewport_size[0] == 250
-    assert viewport_size[1] == 300
+        assert viewport_size[0] == 251
+        assert viewport_size[1] == 301
+    finally:
+        driver.browsing_context.set_viewport(context=context_id, viewport=None, device_pixel_ratio=None)
 
 
 def test_set_viewport_with_device_pixel_ratio(driver, pages):
@@ -361,18 +364,70 @@ def test_set_viewport_with_device_pixel_ratio(driver, pages):
     context_id = driver.current_window_handle
     driver.get(pages.url("formPage.html"))
 
-    driver.browsing_context.set_viewport(
-        context=context_id, viewport={"width": 250, "height": 300}, device_pixel_ratio=5
-    )
+    try:
+        driver.browsing_context.set_viewport(
+            context=context_id, viewport={"width": 252, "height": 302}, device_pixel_ratio=5
+        )
+
+        viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
+
+        assert viewport_size[0] == 252
+        assert viewport_size[1] == 302
+
+        device_pixel_ratio = driver.execute_script("return window.devicePixelRatio")
+
+        assert device_pixel_ratio == 5
+    finally:
+        driver.browsing_context.set_viewport(context=context_id, viewport=None, device_pixel_ratio=None)
+
+
+def test_set_viewport_with_no_args_doesnt_change_values(driver, pages):
+    """Test setting the viewport with no args doesn't change viewport or device pixel ratio."""
+    context_id = driver.current_window_handle
+    driver.get(pages.url("formPage.html"))
+
+    try:
+        driver.browsing_context.set_viewport(
+            context=context_id, viewport={"width": 253, "height": 303}, device_pixel_ratio=6
+        )
+
+        driver.browsing_context.set_viewport(context=context_id)
+
+        viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
+
+        assert viewport_size[0] == 253
+        assert viewport_size[1] == 303
+
+        device_pixel_ratio = driver.execute_script("return window.devicePixelRatio")
+
+        assert device_pixel_ratio == 6
+    finally:
+        driver.browsing_context.set_viewport(context=context_id, viewport=None, device_pixel_ratio=None)
 
-    viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
 
-    assert viewport_size[0] == 250
-    assert viewport_size[1] == 300
+def test_set_viewport_back_to_default(driver, pages):
+    """Test resetting the viewport and device pixel ratio to defaults."""
+    context_id = driver.current_window_handle
+    driver.get(pages.url("formPage.html"))
+
+    default_viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
+    default_device_pixel_ratio = driver.execute_script("return window.devicePixelRatio")
+
+    try:
+        driver.browsing_context.set_viewport(
+            context=context_id, viewport={"width": 254, "height": 304}, device_pixel_ratio=10
+        )
+
+        driver.browsing_context.set_viewport(context=context_id, viewport=None, device_pixel_ratio=None)
 
-    device_pixel_ratio = driver.execute_script("return window.devicePixelRatio")
+        viewport_size = driver.execute_script("return [window.innerWidth, window.innerHeight];")
+        device_pixel_ratio = driver.execute_script("return window.devicePixelRatio")
 
-    assert device_pixel_ratio == 5
+        assert viewport_size[0] == default_viewport_size[0]
+        assert viewport_size[1] == default_viewport_size[1]
+        assert device_pixel_ratio == default_device_pixel_ratio
+    finally:
+        driver.browsing_context.set_viewport(context=context_id, viewport=None, device_pixel_ratio=None)
 
 
 def test_print_page(driver, pages):