diff --git a/src/Protocol/PortableContact.php b/src/Protocol/PortableContact.php
index fb8b48d7c..e2d902ac5 100644
--- a/src/Protocol/PortableContact.php
+++ b/src/Protocol/PortableContact.php
@@ -1375,7 +1375,12 @@ class PortableContact
 					}
 
 					$info = $data['info'];
-					$register_policy = constant($data['register_policy']);
+					if (in_array($data['register_policy'], ['REGISTER_CLOSED', 'REGISTER_APPROVE', 'REGISTER_OPEN'])) {
+						$register_policy = constant($data['register_policy']);
+					} else {
+						Logger::log("Register policy '".$data['register_policy']."' from $server_url is invalid.");
+						$register_policy = REGISTER_CLOSED; // set a default value
+					}
 					$platform = $data['platform'];
 				}
 			}