--- a/mercurial/commands.py	Thu Mar 10 13:43:47 2011 +0100
+++ b/mercurial/commands.py	Thu Mar 10 16:49:37 2011 +0100
@@ -1175,6 +1175,7 @@
         if len(items) > 1 or items and sections:
             raise util.Abort(_('only one config item permitted'))
     for section, name, value in ui.walkconfig(untrusted=untrusted):
+        value = str(value).replace('\n', '\\n')
         sectname = section + '.' + name
         if values:
             for v in values: