diff --git a/hc/accounts/tests/test_project.py b/hc/accounts/tests/test_project.py
index a2032d58..101d8f56 100644
--- a/hc/accounts/tests/test_project.py
+++ b/hc/accounts/tests/test_project.py
@@ -1,8 +1,10 @@
 from django.core import mail
 
 from django.conf import settings
+from django.test.utils import override_settings
 from hc.test import BaseTestCase
 from hc.accounts.models import Member
+from hc.api.models import TokenBucket
 
 
 class ProjectTestCase(BaseTestCase):
@@ -83,6 +85,20 @@ class ProjectTestCase(BaseTestCase):
                 " Alice's Project on %s" % settings.SITE_NAME)
         self.assertEqual(mail.outbox[0].subject, subj)
 
+    @override_settings(SECRET_KEY="test-secret")
+    def test_it_rate_limits_invites(self):
+        obj = TokenBucket(value="invite-%d" % self.alice.id)
+        obj.tokens = 0
+        obj.save()
+
+        self.client.login(username="alice@example.org", password="password")
+
+        form = {"invite_team_member": "1", "email": "frank@example.org"}
+        r = self.client.post(self.url, form)
+        self.assertContains(r, "Too Many Requests")
+
+        self.assertEqual(len(mail.outbox), 0)
+
     def test_it_requires_owner_to_add_team_member(self):
         self.client.login(username="bob@example.org", password="password")
 
diff --git a/hc/accounts/views.py b/hc/accounts/views.py
index f12e9a84..ef2f9602 100644
--- a/hc/accounts/views.py
+++ b/hc/accounts/views.py
@@ -285,6 +285,8 @@ def project(request, code):
 
             form = InviteTeamMemberForm(request.POST)
             if form.is_valid():
+                if not TokenBucket.authorize_invite(request.user):
+                    return render(request, "try_later.html")
 
                 email = form.cleaned_data["email"]
                 try:
diff --git a/hc/api/models.py b/hc/api/models.py
index 326cb636..d0d3d0da 100644
--- a/hc/api/models.py
+++ b/hc/api/models.py
@@ -632,7 +632,7 @@ class TokenBucket(models.Model):
         salted_encoded = (email + settings.SECRET_KEY).encode()
         value = "em-%s" % hashlib.sha1(salted_encoded).hexdigest()
 
-        # 20 emails per 3600 seconds (1 hour):
+        # 20 login attempts for a single email per hour:
         return TokenBucket.authorize(value, 20, 3600)
 
     @staticmethod
@@ -643,5 +643,12 @@ class TokenBucket(models.Model):
         salted_encoded = (ip + settings.SECRET_KEY).encode()
         value = "ip-%s" % hashlib.sha1(salted_encoded).hexdigest()
 
-        # 20 login attempts from a single IP per 3600 seconds (1 hour):
+        # 20 login attempts from a single IP per hour:
         return TokenBucket.authorize(value, 20, 3600)
+
+    @staticmethod
+    def authorize_invite(user):
+        value = "invite-%d" % user.id
+
+        # 20 invites per day
+        return TokenBucket.authorize(value, 20, 3600 * 24)