diff --git a/src/Signup.js b/src/Signup.js
index 42468959fe..fbc2a09634 100644
--- a/src/Signup.js
+++ b/src/Signup.js
@@ -152,6 +152,8 @@ class Register extends Signup {
             } else {
                 if (error.errcode === 'M_USER_IN_USE') {
                     throw new Error("Username in use");
+                } else if (error.errcode == 'M_INVALID_USERNAME') {
+                    throw new Error("User names may only contain alphanumeric characters, underscores or dots!");
                 } else if (error.httpStatus == 401) {
                     throw new Error("Authorisation failed!");
                 } else if (error.httpStatus >= 400 && error.httpStatus < 500) {