diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -168,9 +168,9 @@ if _dowarn:
     # However, module name set through PYTHONWARNINGS was exactly matched, so
     # we cannot set 'mercurial' and have it match eg: 'mercurial.scmutil'. This
     # makes the whole PYTHONWARNINGS thing useless for our usecase.
-    warnings.filterwarnings('default', '', DeprecationWarning, 'mercurial')
-    warnings.filterwarnings('default', '', DeprecationWarning, 'hgext')
-    warnings.filterwarnings('default', '', DeprecationWarning, 'hgext3rd')
+    warnings.filterwarnings(r'default', r'', DeprecationWarning, r'mercurial')
+    warnings.filterwarnings(r'default', r'', DeprecationWarning, r'hgext')
+    warnings.filterwarnings(r'default', r'', DeprecationWarning, r'hgext3rd')
 
 def nouideprecwarn(msg, version, stacklevel=1):
     """Issue an python native deprecation warning