diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index 14855bf03..217e94505 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -1654,6 +1654,13 @@ class Key(BaseType):
             return None
 
         try:
-            return keyutils.KeySequence.parse(value)
+            seq = keyutils.KeySequence.parse(value)
         except keyutils.KeyParseError as e:
             raise configexc.ValidationError(value, str(e))
+
+        for info in seq:
+            if Qt.Key_1 <= info.key <= Qt.Key_9 and not info.modifiers:
+                raise configexc.ValidationError(
+                    value, "Numbers are reserved for counts!")
+
+        return seq
diff --git a/tests/unit/config/test_configtypes.py b/tests/unit/config/test_configtypes.py
index c64891e5a..074a54f23 100644
--- a/tests/unit/config/test_configtypes.py
+++ b/tests/unit/config/test_configtypes.py
@@ -2061,13 +2061,16 @@ class TestKey:
     @pytest.mark.parametrize('val, expected', [
         ('gC', keyutils.KeySequence.parse('gC')),
         ('<Control-x>', keyutils.KeySequence.parse('<ctrl+x>')),
+        ('<alt-1>', keyutils.KeySequence.parse('<alt+1>')),
+        ('0', keyutils.KeySequence.parse('0')),
     ])
     def test_to_py_valid(self, klass, val, expected):
         assert klass().to_py(val) == expected
 
-    def test_to_py_invalid(self, klass):
+    @pytest.mark.parametrize('val', ['\U00010000', '<blub>', '1', 'a1'])
+    def test_to_py_invalid(self, klass, val):
         with pytest.raises(configexc.ValidationError):
-            klass().to_py('\U00010000')
+            klass().to_py(val)
 
 
 @pytest.mark.parametrize('first, second, equal', [