diff --git a/pelican/tests/test_settings.py b/pelican/tests/test_settings.py
index bb05e2ae..a92cf09c 100644
--- a/pelican/tests/test_settings.py
+++ b/pelican/tests/test_settings.py
@@ -285,3 +285,14 @@ class TestSettingsConfiguration(unittest.TestCase):
         self.assertEqual(settings['AUTHOR_REGEX_SUBSTITUTIONS'],
                          [(r'Alexander\ Todorov', 'atodorov')] +
                          default_slug_regex_subs)
+
+    def test_deprecated_slug_substitutions_from_file(self):
+        # This is equivalent to reading a settings file that has
+        # SLUG_SUBSTITUTIONS defined but no SLUG_REGEX_SUBSTITUTIONS.
+        settings = read_settings(None, override={
+            'SLUG_SUBSTITUTIONS': [('C++', 'cpp')]
+        })
+        self.assertEqual(settings['SLUG_REGEX_SUBSTITUTIONS'],
+                         [(r'C\+\+', 'cpp')] +
+                         self.settings['SLUG_REGEX_SUBSTITUTIONS'])
+        self.assertNotIn('SLUG_SUBSTITUTIONS', settings)