diff --git a/tests/test_strict_schema_default_refs.py b/tests/test_strict_schema_default_refs.py
new file mode 100644
index 0000000000..089899b5f4
--- /dev/null
+++ b/tests/test_strict_schema_default_refs.py
@@ -0,0 +1,23 @@
+import copy
+
+from agents.strict_schema import ensure_strict_json_schema
+
+
+def test_default_none_is_removed_from_referenced_property():
+    schema = {
+        "$defs": {
+            "Value": {
+                "type": "string",
+                "default": None,
+            }
+        },
+        "type": "object",
+        "properties": {
+            "value": {"$ref": "#/$defs/Value"},
+        },
+    }
+
+    result = ensure_strict_json_schema(copy.deepcopy(schema))
+
+    assert result["$defs"]["Value"] == {"type": "string"}
+    assert result["properties"]["value"] == {"$ref": "#/$defs/Value"}