diff --git a/src/calibre/test_build.py b/src/calibre/test_build.py
index 9d80091f63..4cd743ecc2 100644
--- a/src/calibre/test_build.py
+++ b/src/calibre/test_build.py
@@ -43,6 +43,7 @@ class BuildTest(unittest.TestCase):
     def test_regex(self):
         import regex
         self.assertEqual(regex.findall(r'(?i)(a)(b)', 'ab cd AB 1a1b'), [('a', 'b'), ('A', 'B')])
+        self.assertEqual(regex.escape('a b', literal_spaces=True), 'a b')
 
     def test_chardet(self):
         from chardet import detect