diff --git a/src/class_smtpServer.py b/src/class_smtpServer.py
index c9d52daa..796e30af 100644
--- a/src/class_smtpServer.py
+++ b/src/class_smtpServer.py
@@ -141,7 +141,12 @@ class bitmessageSMTPChannel(asynchat.async_chat):
             self.push('250 %s' % self.__fqdn)
 
     def smtp_AUTH(self, arg):
-        encoding, pw = arg.split(' ')
+        try:
+            encoding, pw = arg.split(' ')
+        except ValueError:
+            self.invalid_command('501 Syntax: AUTH PLAIN auth')
+            return
+
         if encoding != 'PLAIN':
             self.invalid_command('501 method not understood')
             return