diff --git a/actions/apiaccountregister.php b/actions/apiaccountregister.php
index 9926fc8cf9..b5481df1cb 100644
--- a/actions/apiaccountregister.php
+++ b/actions/apiaccountregister.php
@@ -163,8 +163,8 @@ class ApiAccountRegisterAction extends ApiAction
 	                                                'homepage' => $homepage,
 	                                                'bio' => $bio,
 	                                                'location' => $location,
-	                                                'code' => $code))) {
-	            if (!$user) {
+	                                                'code' => $this->code))) {
+	            if (!$user instanceof User) {
 	                // TRANS: Form validation error displayed when trying to register with an invalid username or password.
 	                $this->clientError(_('Invalid username or password.'), 400);
 	            }
diff --git a/actions/register.php b/actions/register.php
index 82fb9fc573..c97201b666 100644
--- a/actions/register.php
+++ b/actions/register.php
@@ -64,7 +64,7 @@ class RegisterAction extends Action
      * @param $args
      * @return string title
      */
-    function prepare($args)
+    protected function prepare(array $args=array())
     {
         parent::prepare($args);
         $this->code = $this->trimmed('code');
@@ -83,7 +83,7 @@ class RegisterAction extends Action
 
         if (!empty($this->code)) {
             $this->invite = Invitation::getKV('code', $this->code);
-            if (empty($this->invite)) {
+            if (!$this->invite instanceof Invitation) {
             // TRANS: Client error displayed when trying to register to an invite-only site without a valid invitation.
                 $this->clientError(_('Sorry, invalid invitation code.'));
             }
diff --git a/classes/User.php b/classes/User.php
index 1ccbdbc217..bed702867b 100644
--- a/classes/User.php
+++ b/classes/User.php
@@ -276,7 +276,7 @@ class User extends Managed_DataObject
 
         if (!empty($code)) {
             $invite = Invitation::getKV($code);
-            if ($invite && $invite->address && $invite->address_type == 'email' && $invite->address == $email) {
+            if ($invite instanceof Invitation && $invite->address && $invite->address_type == 'email' && $invite->address == $email) {
                 $user->email = $invite->address;
             }
         }