diff --git a/tests/test_convert_to_pdfa.py b/tests/test_convert_to_pdfa.py
index 734ca988..58564289 100644
--- a/tests/test_convert_to_pdfa.py
+++ b/tests/test_convert_to_pdfa.py
@@ -77,6 +77,8 @@ class TestConvertPdfToPdfa:
             _convert_pdf_to_pdfa("/input.pdf", "/output.pdf", fmt)
             cmd = mock_run.call_args[0][0]
             assert f"pdfa-{fmt}" in cmd
+            assert "--" in cmd
+            assert cmd.index("--") < cmd.index("/input.pdf")
 
     def test_invalid_pdfa_format_rejected(self):
         """Test that invalid PDF/A format values are rejected."""