diff --git a/app/models/invite.rb b/app/models/invite.rb
index e64f4c69bd2..1594a109ab4 100644
--- a/app/models/invite.rb
+++ b/app/models/invite.rb
@@ -32,7 +32,7 @@ class Invite < ActiveRecord::Base
   validates :email, email: true, allow_blank: true
   validate :ensure_max_redemptions_allowed
   validate :valid_domain, if: :will_save_change_to_domain?
-  validate :user_doesnt_already_exist
+  validate :user_doesnt_already_exist, if: :will_save_change_to_email?
 
   before_create do
     self.invite_key ||= SecureRandom.base58(10)
diff --git a/spec/requests/omniauth_callbacks_controller_spec.rb b/spec/requests/omniauth_callbacks_controller_spec.rb
index 4f7cbd4fe07..46f81b1d997 100644
--- a/spec/requests/omniauth_callbacks_controller_spec.rb
+++ b/spec/requests/omniauth_callbacks_controller_spec.rb
@@ -411,6 +411,20 @@ RSpec.describe Users::OmniauthCallbacksController do
         expect(user.confirm_password?("securepassword")).to eq(false)
       end
 
+      it "should work if the user has no email_tokens, and an invite" do
+        # Confirming existing email_tokens has a side effect of redeeming invites.
+        # Pretend we don't have any email_tokens
+        user.email_tokens.destroy_all
+
+        invite = Fabricate(:invite, invited_by: Fabricate(:admin))
+        invite.update_column(:email, user.email) # (avoid validation)
+
+        get "/auth/google_oauth2/callback.json"
+        expect(response.status).to eq(302)
+
+        expect(invite.reload.invalidated_at).not_to eq(nil)
+      end
+
       it "should update name/username/email when SiteSetting.auth_overrides_* are enabled" do
         SiteSetting.email_editable = false
         SiteSetting.auth_overrides_email = true