diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -1620,11 +1620,15 @@
         else:
             curframe = inspect.currentframe()
             calframe = inspect.getouterframes(curframe, 2)
-            self.write_err('%s at: %s:%s (%s)\n'
-                           % ((msg,) + calframe[stacklevel][1:4]))
+            frameinfo = calframe[stacklevel]
+
+            self.write_err('%s at: %s:%s (%s)\n' % (
+                msg, frameinfo.filename, frameinfo.lineno,
+                frameinfo.function))
             self.log('develwarn', '%s at: %s:%s (%s)\n',
-                     msg, *calframe[stacklevel][1:4])
-            curframe = calframe = None  # avoid cycles
+                     msg, frameinfo.filename, frameinfo.lineno,
+                     frameinfo.function)
+            curframe = calframe = frameinfo = None  # avoid cycles
 
     def deprecwarn(self, msg, version, stacklevel=2):
         """issue a deprecation warning