diff --git a/erpnext/crm/doctype/opportunity/opportunity.py b/erpnext/crm/doctype/opportunity/opportunity.py
index 4d4593641a8..adac8f59222 100644
--- a/erpnext/crm/doctype/opportunity/opportunity.py
+++ b/erpnext/crm/doctype/opportunity/opportunity.py
@@ -342,7 +342,7 @@ def assign_to_user(doc, subject_field):
 	elif doc.lead:
 		assign_user = frappe.db.get_value('Lead', doc.lead, 'lead_owner')
 
-	if assign_user and assign_user != 'Administrator':
+	if assign_user and assign_user not in ['Administrator', 'Guest']:
 		if not assign_to.get(dict(doctype = doc.doctype, name = doc.name)):
 			assign_to.add({
 				"assign_to": assign_user,