diff --git a/scripts/security/gitea-authenticated-inventory-payload-validator.py b/scripts/security/gitea-authenticated-inventory-payload-validator.py
index d654274e..c41bdc43 100644
--- a/scripts/security/gitea-authenticated-inventory-payload-validator.py
+++ b/scripts/security/gitea-authenticated-inventory-payload-validator.py
@@ -260,6 +260,8 @@ def main() -> int:
     validation = validate_payload(load_json(args.input))
     text = json.dumps(validation, ensure_ascii=False, indent=2) + "\n"
     if args.output:
+        if args.output.resolve() == args.input.resolve():
+            raise SystemExit("output_must_not_equal_input")
         args.output.parent.mkdir(parents=True, exist_ok=True)
         args.output.write_text(text, encoding="utf-8")
     else:
diff --git a/scripts/security/tests/test_gitea_authenticated_inventory_payload_validator.py b/scripts/security/tests/test_gitea_authenticated_inventory_payload_validator.py
index 45c300a1..92a95db2 100644
--- a/scripts/security/tests/test_gitea_authenticated_inventory_payload_validator.py
+++ b/scripts/security/tests/test_gitea_authenticated_inventory_payload_validator.py
@@ -72,6 +72,30 @@ def test_rejects_execution_request(tmp_path: Path) -> None:
     assert validation["operation_boundaries"]["gitea_write_performed"] is False
 
 
+def test_output_must_not_overwrite_input(tmp_path: Path) -> None:
+    payload_path = tmp_path / "inventory.json"
+    original = json.dumps(valid_payload())
+    payload_path.write_text(original, encoding="utf-8")
+
+    result = subprocess.run(
+        [
+            sys.executable,
+            str(SCRIPT),
+            "--input",
+            str(payload_path),
+            "--output",
+            str(payload_path),
+        ],
+        text=True,
+        capture_output=True,
+        check=False,
+    )
+
+    assert result.returncode != 0
+    assert "output_must_not_equal_input" in result.stderr
+    assert payload_path.read_text(encoding="utf-8") == original
+
+
 def valid_payload() -> dict:
     repos = [
         repo("wooo/awoooi"),