diff --git a/clktc/links/models.py b/clktc/links/models.py
index ee00904..56a5828 100644
--- a/clktc/links/models.py
+++ b/clktc/links/models.py
@@ -1,8 +1,14 @@
 from django.contrib.auth.models import User
 from django.contrib.sites.models import Site
+from django.core.exceptions import ValidationError
 from django.db import models
 
-# Create your models here.
+
+class LinkWithShortUrlAlreadyExistsForSite(ValidationError):
+    def __init__(self):
+        super(LinkWithShortUrlAlreadyExistsForSite, self).__init__({
+            'short_url': ["Link with this short URL already exists for this site. Please try another one."]
+        })
 
 class Link(models.Model):
     destination_url = models.URLField("Destination", max_length=255, blank=False, verify_exists=False)
@@ -17,7 +23,19 @@ class Meta:
     def url(self):
         return "http://%s/%s" % (self.site.domain, self.short_url)
 
+    def is_unique(self, matching):
+        if not len(matching):
+            return True
+        elif self.pk:
+            if len(matching) == 1:
+                other = matching.get()
+                return other.pk == self.pk
+
     def save(self, *args, **kw):
+        if self.short_url and self.site_id:
+            matching = Link.objects.filter(short_url=self.short_url, site=self.site)
+            if not self.is_unique(matching):
+                raise LinkWithShortUrlAlreadyExistsForSite()
         self.full_clean()
         super(Link, self).save(*args, **kw)
 
diff --git a/clktc/links/tests/test_models.py b/clktc/links/tests/test_models.py
index f72158a..350556f 100644
--- a/clktc/links/tests/test_models.py
+++ b/clktc/links/tests/test_models.py
@@ -47,7 +47,7 @@ def test_site_and_short_url_are_unique_together(self):
         Model.save(l1)
         Model.save(l2)
 
-    @raises_regexp(ValidationError, 'Link with this Short URL and Site already exists')
+    @raises_regexp(ValidationError, 'Link with this short URL already exists for this site. Please try another one.')
     def test_site_and_short_url_are_unique_together(self):
         Link(destination_url = "http://example.com", short_url = "foobarbaz", site = self.site).save()
         Link(destination_url = "http://example.com", short_url = "foobarbaz", site = self.site).save()
diff --git a/clktc/links/tests/test_views.py b/clktc/links/tests/test_views.py
index 5fcdaa6..783f0c3 100644
--- a/clktc/links/tests/test_views.py
+++ b/clktc/links/tests/test_views.py
@@ -64,6 +64,12 @@ def test_adding_a_link_without_short_url(self):
         response = self.client.post('/l/add/', {"destination_url" : EXAMPLE_URL, "short_url" : ""})
         self.assertFormError(response, 'form', 'short_url', u'This field is required.')
 
+    def test_adding_a_link_with_duplicate_short_url(self):
+        link = given_a_link(self.site, user=self.user)
+        response = self.client.post('/l/add/', {"destination_url" : "http://foo.bar/baz", "short_url": link.short_url})
+        self.assertFormError(response, 'form', 'short_url', u'Link with this short URL already exists for this site. Please try another one.')
+
+
 class EditLinkTest(ViewBaseTest):
     def test_edit_link_returns_404_if_current_owner_does_not_match(self):
         link = given_a_link(self.site)
@@ -84,7 +90,7 @@ def test_save_on_edit_link_updates_link_with_new_details(self):
     
     def test_save_on_edit_link_redirects_to_all_links(self):
         link = given_a_link(self.site, user=self.user)
-        response = self.client.post("/l/edit/%s" % link.pk, {"destination_url" : "http://example.org", "short_url" : "example2"})
+        response = self.client.post("/l/edit/%s" % link.pk, {"destination_url" : "http://example.org"})
         self.assertRedirects(response, ALL_LINKS)
 
 class VisitLinkTest(ViewBaseTest):
diff --git a/clktc/links/views.py b/clktc/links/views.py
index 937863d..b25422c 100644
--- a/clktc/links/views.py
+++ b/clktc/links/views.py
@@ -1,5 +1,6 @@
 # Create your views here.
 from django.contrib.auth.decorators import login_required
+from django.core.exceptions import ValidationError
 from django.http import  HttpResponseNotAllowed, HttpResponseNotFound
 from django.shortcuts import render_to_response, redirect, get_object_or_404
 from django.template.context import RequestContext
@@ -23,8 +24,11 @@ def add_link(request):
             link = form.save(commit=False)
             link.site = request.site
             link.user = request.user
-            link.save()
-            return redirect(get_all_links)
+            try:
+                link.save()
+                return redirect(get_all_links)
+            except ValidationError as ve:
+                form._update_errors(ve.message_dict)
     else:
         form = AddLinkForm()
     return render_to_response("links/add.html", RequestContext(request, {'form': form}))