diff --git a/tests/async/test_fetch_global.py b/tests/async/test_fetch_global.py
index 6a915fc49..2b6242e2a 100644
--- a/tests/async/test_fetch_global.py
+++ b/tests/async/test_fetch_global.py
@@ -325,3 +325,14 @@ async def test_should_throw_an_error_when_max_redirects_is_less_than_0(
                 server.PREFIX + "/a/redirect1", method=method, max_redirects=-1
             )
         assert "'max_redirects' must be greater than or equal to '0'" in str(exc_info)
+
+
+async def test_should_serialize_null_values_in_json(
+    playwright: Playwright, server: Server
+) -> None:
+    request = await playwright.request.new_context()
+    server.set_route("/echo", lambda req: (req.write(req.post_body), req.finish()))
+    response = await request.post(server.PREFIX + "/echo", data={"foo": None})
+    assert response.status == 200
+    assert await response.text() == '{"foo":null}'
+    await request.dispose()
diff --git a/tests/server.py b/tests/server.py
index 9b486af3c..2bd3e672a 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -196,7 +196,9 @@ def reset(self) -> None:
         self.gzip_routes.clear()
         self.routes.clear()
 
-    def set_route(self, path: str, callback: Callable[[http.Request], Any]) -> None:
+    def set_route(
+        self, path: str, callback: Callable[[HttpRequestWithPostBody], Any]
+    ) -> None:
         self.routes[path] = callback
 
     def enable_gzip(self, path: str) -> None:
diff --git a/tests/sync/test_fetch_global.py b/tests/sync/test_fetch_global.py
index fc30cc00c..a45c207da 100644
--- a/tests/sync/test_fetch_global.py
+++ b/tests/sync/test_fetch_global.py
@@ -235,3 +235,14 @@ def test_should_throw_an_error_when_max_redirects_is_less_than_0(
                 server.PREFIX + "/a/redirect1", method=method, max_redirects=-1
             )
         assert "'max_redirects' must be greater than or equal to '0'" in str(exc_info)
+
+
+def test_should_serialize_null_values_in_json(
+    playwright: Playwright, server: Server
+) -> None:
+    request = playwright.request.new_context()
+    server.set_route("/echo", lambda req: (req.write(req.post_body), req.finish()))
+    response = request.post(server.PREFIX + "/echo", data={"foo": None})
+    assert response.status == 200
+    assert response.text() == '{"foo":null}'
+    request.dispose()