diff --git a/discord/ext/commands/bot.py b/discord/ext/commands/bot.py
index 43254a4d2..33796f98d 100644
--- a/discord/ext/commands/bot.py
+++ b/discord/ext/commands/bot.py
@@ -41,7 +41,7 @@ from .formatter import HelpFormatter
 def when_mentioned(bot, msg):
     """A callable that implements a command prefix equivalent
     to being mentioned, e.g. ``@bot ``."""
-    return [bot.user.mention, '<@!%s>' % bot.user.id]
+    return [bot.user.mention + ' ', '<@!%s> ' % bot.user.id]
 
 def when_mentioned_or(*prefixes):
     """A callable that implements when mentioned or other prefixes provided.