diff --git a/erpnext/controllers/sales_and_purchase_return.py b/erpnext/controllers/sales_and_purchase_return.py
index 7d03722..28dd4ea 100644
--- a/erpnext/controllers/sales_and_purchase_return.py
+++ b/erpnext/controllers/sales_and_purchase_return.py
@@ -24,7 +24,7 @@
 	else:
 		ref_doc = frappe.get_doc(doc.doctype, doc.return_against)
 
-		if ref_doc.company == doc.company and ref_doc.customer = doc.customer and ref_doc.docstatus == 1:
+		if ref_doc.company == doc.company and ref_doc.customer == doc.customer and ref_doc.docstatus == 1:
 			# validate posting date time
 			return_posting_datetime = "%s %s" % (doc.posting_date, doc.get("posting_time") or "00:00:00")
 			ref_posting_datetime = "%s %s" % (ref_doc.posting_date, ref_doc.get("posting_time") or "00:00:00")