diff --git a/flask_security/forms.py b/flask_security/forms.py
index bacf118..b021fb6 100644
--- a/flask_security/forms.py
+++ b/flask_security/forms.py
@@ -21,6 +21,14 @@ from .exceptions import UserNotFoundError
 _datastore = LocalProxy(lambda: app.extensions['security'].datastore)
 
 
+def unique_user_email(form, field):
+    try:
+        _datastore.find_user(email=field.data)
+        raise ValidationError('%s is already associated with an account' % field.data)
+    except UserNotFoundError:
+        pass
+
+
 def valid_user_email(form, field):
     try:
         _datastore.find_user(email=field.data)
@@ -41,6 +49,13 @@ class UserEmailFormMixin():
                     valid_user_email])
 
 
+class UniqueEmailFormMixin():
+    email = TextField("Email Address",
+        validators=[Required(message="Email not provided"),
+                    Email(message="Invalid email address"),
+                    unique_user_email])
+
+
 class PasswordFormMixin():
     password = PasswordField("Password",
         validators=[Required(message="Password not provided")])
@@ -102,7 +117,7 @@ class LoginForm(Form, EmailFormMixin, PasswordFormMixin):
 
 
 class RegisterForm(Form,
-                   EmailFormMixin,
+                   UniqueEmailFormMixin,
                    PasswordFormMixin,
                    PasswordConfirmFormMixin):
     """The default register form"""
diff --git a/tests/functional_tests.py b/tests/functional_tests.py
index b913c64..f8d3ef3 100644
--- a/tests/functional_tests.py
+++ b/tests/functional_tests.py
@@ -237,9 +237,16 @@ class ConfiguredSecurityTests(SecurityTest):
                     password='password',
                     password_confirm='password')
 
-        r = self.client.post('/register', data=data, follow_redirects=True)
+        r = self._post('/register', data=data, follow_redirects=True)
         self.assertIn('Post Register', r.data)
 
+    def test_register_existing_email(self):
+        data = dict(email='matt@lp.com',
+                    password='password',
+                    password_confirm='password')
+        r = self._post('/register', data=data, follow_redirects=True)
+        self.assertIn('matt@lp.com is already associated with an account', r.data)
+
     def test_unauthorized(self):
         self.authenticate("joe@lp.com", endpoint="/custom_auth")
         r = self._get("/admin", follow_redirects=True)