diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index c15de3d0f..4ad5037f4 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -46,6 +46,12 @@ BOOLEAN_STATES = {'1': True, 'yes': True, 'true': True, 'on': True,
 
 
 def _validate_regex(pattern, flags):
+    """Check if the given regex is valid.
+
+    This is more complicated than it could be since there's a warning on
+    invalid escapes with newer Python versions, and we want to catch that case
+    and treat it as invalid.
+    """
     with warnings.catch_warnings(record=True) as recorded_warnings:
         warnings.simplefilter('always')
         try:
diff --git a/tests/unit/config/test_configtypes.py b/tests/unit/config/test_configtypes.py
index a6d328ea4..2b3b44485 100644
--- a/tests/unit/config/test_configtypes.py
+++ b/tests/unit/config/test_configtypes.py
@@ -1092,12 +1092,29 @@ class TestRegex:
         Warning('foo'), DeprecationWarning('foo'),
     ])
     def test_passed_warnings(self, mocker, klass, warning):
+        """Simulate re.compile showing a warning we don't know about yet.
+
+        The warning should be passed.
+        """
         m = mocker.patch('qutebrowser.config.configtypes.re')
         m.compile.side_effect = lambda *args: warnings.warn(warning)
         m.error = re.error
         with pytest.raises(type(warning)):
             klass().validate('foo')
 
+    def test_bad_pattern_warning(self, mocker, klass):
+        """Test a simulated bad pattern warning.
+
+        This only seems to happen with Python 3.5, so we simulate this for
+        better coverage.
+        """
+        m = mocker.patch('qutebrowser.config.configtypes.re')
+        m.compile.side_effect = lambda *args: warnings.warn(r'bad escape \C',
+                                                            DeprecationWarning)
+        m.error = re.error
+        with pytest.raises(configexc.ValidationError):
+            klass().validate('foo')
+
 
 class TestRegexList: