diff --git a/playwright/_impl/_fetch.py b/playwright/_impl/_fetch.py
index 6181f22b2..e8b812b92 100644
--- a/playwright/_impl/_fetch.py
+++ b/playwright/_impl/_fetch.py
@@ -395,7 +395,11 @@ async def _inner_fetch(
             elif isinstance(data, bytes):
                 post_data_buffer = data
             elif isinstance(data, (dict, list, int, bool)):
-                json_data = json.dumps(data)
+                try:
+                    # NaN and Infinity are not valid JSON.
+                    json_data = json.dumps(data, allow_nan=False)
+                except ValueError as e:
+                    raise Error(str(e)) from None
             else:
                 raise Error(f"Unsupported 'data' type: {type(data)}")
         elif form:
diff --git a/tests/async/test_fetch_global.py b/tests/async/test_fetch_global.py
index 10f82583c..e09567f71 100644
--- a/tests/async/test_fetch_global.py
+++ b/tests/async/test_fetch_global.py
@@ -474,6 +474,16 @@ async def test_should_serialize_request_data(
     await request.dispose()
 
 
+@pytest.mark.parametrize("value", [float("inf"), float("-inf"), float("nan")])
+async def test_should_reject_non_finite_floats_in_request_data(
+    playwright: Playwright, server: Server, value: float
+) -> None:
+    request = await playwright.request.new_context()
+    with pytest.raises(Error, match="Out of range float values are not JSON"):
+        await request.post(server.EMPTY_PAGE, data={"value": value})
+    await request.dispose()
+
+
 async def test_should_retry_ECONNRESET(playwright: Playwright, server: Server) -> None:
     request_count = 0
 
diff --git a/tests/sync/test_fetch_global.py b/tests/sync/test_fetch_global.py
index 15a11fca8..ffc91be60 100644
--- a/tests/sync/test_fetch_global.py
+++ b/tests/sync/test_fetch_global.py
@@ -334,6 +334,16 @@ def test_should_serialize_null_values_in_json(
     request.dispose()
 
 
+@pytest.mark.parametrize("value", [float("inf"), float("-inf"), float("nan")])
+def test_should_reject_non_finite_floats_in_request_data(
+    playwright: Playwright, server: Server, value: float
+) -> None:
+    request = playwright.request.new_context()
+    with pytest.raises(Error, match="Out of range float values are not JSON"):
+        request.post(server.EMPTY_PAGE, data={"value": value})
+    request.dispose()
+
+
 def test_should_throw_when_fail_on_status_code_is_true(
     playwright: Playwright, server: Server
 ) -> None: