diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -92,13 +92,8 @@ def _formatparse(write, inst):
     if inst.hint:
         write(_("(%s)\n") % inst.hint)
 
-def _mayberepr(a):
-    if ' ' in a:
-        return encoding.strtolocal(repr(a))
-    return a
-
 def _formatargs(args):
-    return ' '.join(_mayberepr(a) for a in args)
+    return ' '.join(util.shellquote(a) for a in args)
 
 def dispatch(req):
     "run the command specified in req.args"
diff --git a/tests/test-blackbox.t b/tests/test-blackbox.t
--- a/tests/test-blackbox.t
+++ b/tests/test-blackbox.t
@@ -25,7 +25,7 @@ alias expansion is logged
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000 (5000)> add a
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000 (5000)> add a exited 0 after * seconds (glob)
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000+ (5000)> blackbox
-  1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000+ (5000)> blackbox --config blackbox.dirty=True exited 0 after * seconds (glob)
+  1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000+ (5000)> blackbox --config 'blackbox.dirty=True' exited 0 after * seconds (glob)
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000 (5000)> confuse
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000 (5000)> alias 'confuse' expands to 'log --limit 3'
   1970/01/01 00:00:00 bob @0000000000000000000000000000000000000000 (5000)> confuse exited 0 after * seconds (glob)
diff --git a/tests/test-devel-warnings.t b/tests/test-devel-warnings.t
--- a/tests/test-devel-warnings.t
+++ b/tests/test-devel-warnings.t
@@ -139,7 +139,7 @@
   $ hg blackbox -l 9
   1970/01/01 00:00:00 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: revset "oldstyle" uses list instead of smartset
   (compatibility will be dropped after Mercurial-3.9, update your code.) at: *mercurial/revset.py:* (mfunc) (glob)
-  1970/01/01 00:00:00 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> log -r oldstyle() -T {rev}\n exited 0 after * seconds (glob)
+  1970/01/01 00:00:00 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> log -r 'oldstyle()' -T '{rev}\n' exited 0 after * seconds (glob)
   1970/01/01 00:00:00 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated
   1970/01/01 00:00:00 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
   (compatibility will be dropped after Mercurial-42.1337, update your code.) at: $TESTTMP/buggylocking.py:* (oldanddeprecated) (glob)