diff --git a/qutebrowser/commands/cmdutils.py b/qutebrowser/commands/cmdutils.py
index 5e77aeaca..398bbed32 100644
--- a/qutebrowser/commands/cmdutils.py
+++ b/qutebrowser/commands/cmdutils.py
@@ -224,6 +224,9 @@ class register:  # pylint: disable=invalid-name
         if 'self' in signature.parameters and self.instance is None:
             raise TypeError("{} is a class method, but instance was not "
                             "given!".format(self.name[0]))
+        elif 'self' not in signature.parameters and self.instance is not None:
+            raise TypeError("{} is not a class method, but instance was "
+                            "given!".format(self.name[0]))
         has_count = 'count' in signature.parameters
         doc = inspect.getdoc(self.func)
         if doc is not None: