diff --git a/frappe/core/doctype/user/user.py b/frappe/core/doctype/user/user.py
index 00cc5184f3..286adbc441 100644
--- a/frappe/core/doctype/user/user.py
+++ b/frappe/core/doctype/user/user.py
@@ -316,7 +316,8 @@ class User(Document):
 
 		# should be made up of characters, numbers and underscore only
 		if not re.match(r"^[\w]+$", self.username):
-			frappe.throw(_("Username should not contain any special characters other than letters, numbers and underscore"))
+			frappe.msgprint(_("Username should not contain any special characters other than letters, numbers and underscore"))
+			self.username = ""
 
 	def suggest_username(self):
 		def _check_suggestion(suggestion):
diff --git a/frappe/patches/v6_15/set_username.py b/frappe/patches/v6_15/set_username.py
index bd787cffe1..4e62cad178 100644
--- a/frappe/patches/v6_15/set_username.py
+++ b/frappe/patches/v6_15/set_username.py
@@ -7,7 +7,7 @@ def execute():
 	users = frappe.db.sql_list("""select name from `tabUser` order by if(user_type='System User', 0, 1)""")
 	for name in users:
 		user = frappe.get_doc("User", name)
-		if user.username:
+		if user.username or not user.first_name:
 			continue
 
 		username = user.suggest_username()