diff --git a/colab/accounts/auth.py b/colab/accounts/auth.py
index 9500fbd..4ccda35 100644
--- a/colab/accounts/auth.py
+++ b/colab/accounts/auth.py
@@ -14,7 +14,7 @@ class ColabBrowserIDBackend(BrowserIDBackend):
 
         user = self.User.objects.filter(emails__address=email)
 
-        if not user:
+        if user:
             return user
 
         return self.User.objects.create_user(
diff --git a/colab/accounts/forms.py b/colab/accounts/forms.py
index fcb6a75..c871a94 100644
--- a/colab/accounts/forms.py
+++ b/colab/accounts/forms.py
@@ -55,6 +55,19 @@ class UserCreationForm(UserForm):
         widget=forms.TextInput(attrs={'readonly': 'readonly'})
     )
 
+    def __init__(self, *args, **kwargs):
+        self.original_email = kwargs.pop('email', None)
+        super(UserCreationForm, self).__init__(*args, **kwargs)
+
+    def clean_email(self):
+        form_email = self.cleaned_data['email']
+
+        if form_email != self.original_email:
+            raise forms.ValidationError('This is not the original email.')
+
+        return form_email
+
+
     def clean_username(self):
         username = self.cleaned_data['username']
         username = username.strip()
--
libgit2 0.21.2