diff --git a/tests/test_nlp_cner.py b/tests/test_nlp_cner.py
index d65eac4..d5f416a 100644
--- a/tests/test_nlp_cner.py
+++ b/tests/test_nlp_cner.py
@@ -66,6 +66,7 @@ def test_prompt_tag(self):
         self.assertEqual(self.ner.prompt_tag('NCF'), 'is_likely_abbreviation')
         self.assertEqual(self.ner.prompt_tag('EC300J'), 'other')
         self.assertEqual(self.ner.prompt_tag('PC'), 'other')
+        self.assertEqual(self.ner.prompt_tag('C4H4O6KNa·4H2O'), 'synthetic')
         self.assertEqual(self.ner.prompt_tag('PO4'), 'polyatomic_ions')
         self.assertEqual(self.ner.prompt_tag('Na-ion'), 'other')
         self.assertEqual(self.ner.prompt_tag('Na-N532'), 'is_likely_abbreviation')