diff --git a/gratipay/exceptions.py b/gratipay/exceptions.py
index ac33104056..87494773f0 100644
--- a/gratipay/exceptions.py
+++ b/gratipay/exceptions.py
@@ -57,6 +57,7 @@ class NoSelfTipping(Exception): pass
 class NoTippee(Exception): pass
 class NoTeam(Exception): pass
 class BadAmount(Exception): pass
+class InvalidTeamName(Exception): pass
 
 class FailedToReserveUsername(Exception): pass
 
diff --git a/gratipay/models/team.py b/gratipay/models/team.py
index adac4208e8..d149ac6985 100644
--- a/gratipay/models/team.py
+++ b/gratipay/models/team.py
@@ -1,10 +1,28 @@
 """Teams on Gratipay receive payments and distribute payroll.
 """
+import re
 import requests
 from aspen import json, log
+from gratipay.exceptions import InvalidTeamName
 from gratipay.models import add_event
 from postgres.orm import Model
 
+# Should have at least one alphabet.
+TEAM_NAME_PATTERN = re.compile(r'^(?=.*[A-Za-z])([A-Za-z0-9.,-_ ]+)$')
+
+def slugize(name):
+    """ Create a slug from a team name.
+    """
+    if TEAM_NAME_PATTERN.match(name) is None:
+      raise InvalidTeamName
+
+    slug = name.strip()
+    for c in (',', ' '):
+        slug = slug.replace(c, '-') # Avoid % encoded characters in slug url.
+    while '--' in slug:
+        slug = slug.replace('--', '-')
+    slug = slug.strip('-')
+    return slug
 
 class Team(Model):
     """Represent a Gratipay team.
diff --git a/www/teams/create.json.spt b/www/teams/create.json.spt
index 5a6a510c93..a294633e3b 100644
--- a/www/teams/create.json.spt
+++ b/www/teams/create.json.spt
@@ -72,7 +72,7 @@ if request.method == 'POST':
 
     try:
         fields['slug'] = slugize(fields['name'])
-    except AssertionError:
+    except InvalidTeamName:
         raise Response(400, _("Sorry, team name contains invalid characters."))
 
     try: