diff --git a/modoboa/auth/lib.py b/modoboa/auth/lib.py
index 38e95382d..8808cd240 100644
--- a/modoboa/auth/lib.py
+++ b/modoboa/auth/lib.py
@@ -12,7 +12,7 @@ def random_key(l=16):
     :param integer l: the key's length
     :return: a string
     """
-    char_set = string.printable
+    char_set = string.digits + string.letters + string.punctuation
     return ''.join(random.sample(char_set * l, l))