diff --git a/sphinx/domains/python.py b/sphinx/domains/python.py
index 051da4480..402bdfc9f 100644
--- a/sphinx/domains/python.py
+++ b/sphinx/domains/python.py
@@ -496,10 +496,12 @@ class PyObject(ObjectDescription[Tuple[str, str]]):
         sig_prefix = self.get_signature_prefix(sig)
         if sig_prefix:
             if type(sig_prefix) is str:
-                logger.warning("Python directive get_signature_prefix() returns a str ('{}')"
-                               " instead of a list of nodes (changed in 4.3).".format(sig_prefix),
-                               location=signode)
-                signode += addnodes.desc_annotation(sig_prefix, '', nodes.Text(sig_prefix, sig_prefix))
+                logger.warning(
+                    "Python directive get_signature_prefix() returns a str ('{}')"
+                    " instead of a list of nodes (changed in 4.3).".format(sig_prefix),
+                    location=signode)
+                signode += addnodes.desc_annotation(sig_prefix, '',  # type: ignore
+                                                    nodes.Text(sig_prefix))  # type: ignore
             else:
                 signode += addnodes.desc_annotation(str(sig_prefix), '', *sig_prefix)