diff --git a/qutebrowser/commands/command.py b/qutebrowser/commands/command.py
index 9048ea4e0..802d4a4bb 100644
--- a/qutebrowser/commands/command.py
+++ b/qutebrowser/commands/command.py
@@ -40,6 +40,8 @@ class ArgInfo:
     """Information about an argument."""
 
     def __init__(self, win_id=False, count=False, flag=None):
+        if win_id and count:
+            raise TypeError("Argument marked as both count/win_id!")
         self.win_id = win_id
         self.count = count
         self.flag = flag
diff --git a/tests/unit/commands/test_cmdutils.py b/tests/unit/commands/test_cmdutils.py
index 6a4bc829b..1fa47d556 100644
--- a/tests/unit/commands/test_cmdutils.py
+++ b/tests/unit/commands/test_cmdutils.py
@@ -294,3 +294,12 @@ class TestArgument:
                 "@cmdutils.register for fun!")
 
         assert str(excinfo.value) == text
+
+    def test_count_and_win_id_same_arg(self):
+        with pytest.raises(TypeError) as excinfo:
+            @cmdutils.argument('arg', count=True, win_id=True)
+            def fun(arg=0):
+                """Blah."""
+                pass
+
+        assert str(excinfo.value) == "Argument marked as both count/win_id!"