From d86f0e1e35c8f83aa3ef64d2c4447f497baa89ba Mon Sep 17 00:00:00 2001
From: toby-m121 <toby@propero.app>
Date: Mon, 19 Oct 2026 22:12:23 +1100
Subject: [PATCH] fix: send non-finite float properties as null instead of
 invalid JSON

Closes #1078
---
 .sampo/changesets/non-finite-floats-null.md |  5 +++++
 posthog/test/test_utils.py                  | 17 +++++++++++++++++
 posthog/utils.py                            |  5 ++++-
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 .sampo/changesets/non-finite-floats-null.md

diff --git a/.sampo/changesets/non-finite-floats-null.md b/.sampo/changesets/non-finite-floats-null.md
new file mode 100644
index 000000000..27df049f3
--- /dev/null
+++ b/.sampo/changesets/non-finite-floats-null.md
@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Non-finite float property values (`inf`, `-inf`, `nan`, including `Decimal("Infinity")`) are now sent as `null` instead of the invalid JSON tokens `Infinity`/`NaN`, so strict-parsing ingestion no longer rejects the whole batch. This matches posthog-js.
diff --git a/posthog/test/test_utils.py b/posthog/test/test_utils.py
index e655c8cd5..8440dcae3 100644
--- a/posthog/test/test_utils.py
+++ b/posthog/test/test_utils.py
@@ -250,6 +250,23 @@ def test_clean_fn(self):
         cleaned = utils.clean({"fn": lambda x: x, "number": 4})
         assert cleaned == {"fn": None, "number": 4}
 
+    @parameterized.expand(
+        [
+            ("inf", float("inf"), None),
+            ("negative_inf", float("-inf"), None),
+            ("nan", float("nan"), None),
+            ("decimal_inf", Decimal("Infinity"), None),
+            ("finite_float", 1.5, 1.5),
+            ("finite_decimal", Decimal("1.25"), 1.25),
+        ]
+    )
+    def test_clean_non_finite_floats(self, _name, value, expected):
+        assert utils.clean(value) == expected
+
+    def test_clean_non_finite_floats_nested(self):
+        cleaned = utils.clean({"a": [float("nan"), {"b": float("inf")}], "ok": 2.0})
+        assert cleaned == {"a": [None, {"b": None}], "ok": 2.0}
+
     @parameterized.expand(
         [
             ("http://posthog.io/", "http://posthog.io"),
diff --git a/posthog/utils.py b/posthog/utils.py
index 05608983f..71fa2580f 100644
--- a/posthog/utils.py
+++ b/posthog/utils.py
@@ -1,5 +1,6 @@
 import json
 import logging
+import math
 import numbers
 import re
 import threading
@@ -84,9 +85,11 @@ def remove_trailing_slash(host: str) -> str:
 
 def clean(item):
     if isinstance(item, Decimal):
-        return float(item)
+        return clean(float(item))
     if isinstance(item, UUID):
         return str(item)
+    if isinstance(item, float) and not math.isfinite(item):
+        return None
     if isinstance(item, (str, bool, numbers.Number, datetime, date, type(None))):
         return item
     if isinstance(item, (set, list, tuple)):