diff --git a/erpnext/accounts/doctype/gl_entry/gl_entry.py b/erpnext/accounts/doctype/gl_entry/gl_entry.py
index 47e214e1b48..9cec1c0dc66 100644
--- a/erpnext/accounts/doctype/gl_entry/gl_entry.py
+++ b/erpnext/accounts/doctype/gl_entry/gl_entry.py
@@ -18,15 +18,14 @@ class GLEntry(Document):
 		self.flags.ignore_submit_comment = True
 		self.check_mandatory()
 		self.validate_and_set_fiscal_year()
+		self.pl_must_have_cost_center()
+		self.validate_cost_center()
 
 		if not self.flags.from_repost:
-			self.pl_must_have_cost_center()
 			self.check_pl_account()
-			self.validate_cost_center()
 			self.validate_party()
 			self.validate_currency()
 
-
 	def on_update_with_args(self, adv_adj, update_outstanding = 'Yes', from_repost=False):
 		if not from_repost:
 			self.validate_account_details(adv_adj)
diff --git a/erpnext/regional/india/utils.py b/erpnext/regional/india/utils.py
index b878a1ea5d0..fd0eb34abc9 100644
--- a/erpnext/regional/india/utils.py
+++ b/erpnext/regional/india/utils.py
@@ -8,22 +8,49 @@ def validate_gstin_for_india(doc, method):
 	if not hasattr(doc, 'gstin'):
 		return
 
-	if doc.gstin:
-		doc.gstin = doc.gstin.upper()
-		if doc.gstin not in ["NA", "na"]:
-			p = re.compile("[0-9]{2}[a-zA-Z]{5}[0-9]{4}[a-zA-Z]{1}[1-9A-Za-z]{1}[Z]{1}[0-9a-zA-Z]{1}")
-			if not p.match(doc.gstin):
-				frappe.throw(_("Invalid GSTIN or Enter NA for Unregistered"))
+	doc.gstin = doc.gstin.upper().strip()
+	if not doc.gstin or doc.gstin == 'NA':
+		return
+
+	if len(doc.gstin) != 15:
+		frappe.throw(_("Invalid GSTIN! A GSTIN must have 15 characters."))
+
+	p = re.compile("^[0-9]{2}[A-Z]{4}[0-9A-Z]{1}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}[1-9A-Z]{1}[0-9A-Z]{1}$")
+	if not p.match(doc.gstin):
+		frappe.throw(_("Invalid GSTIN! The input you've entered doesn't match the format of GSTIN."))
+
+	validate_gstin_check_digit(doc.gstin)
 
 	if not doc.gst_state:
-		if doc.state in states:
-			doc.gst_state = doc.state
+		if not doc.state:
+			return
+		state = doc.state.lower()
+		states_lowercase = {s.lower():s for s in states}
+		if state in states_lowercase:
+			doc.gst_state = states_lowercase[state]
+		else:
+			return
 
-	if doc.gst_state:
-		doc.gst_state_number = state_numbers[doc.gst_state]
-		if doc.gstin and doc.gstin != "NA" and doc.gst_state_number != doc.gstin[:2]:
-			frappe.throw(_("First 2 digits of GSTIN should match with State number {0}")
-				.format(doc.gst_state_number))
+	doc.gst_state_number = state_numbers[doc.gst_state]
+	if doc.gst_state_number != doc.gstin[:2]:
+		frappe.throw(_("Invalid GSTIN! First 2 digits of GSTIN should match with State number {0}.")
+			.format(doc.gst_state_number))
+
+def validate_gstin_check_digit(gstin):
+	''' Function to validate the check digit of the GSTIN.'''
+	factor = 1
+	total = 0
+	code_point_chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+	mod = len(code_point_chars)
+	input_chars = gstin[:-1]
+	for char in input_chars:
+		digit = factor * code_point_chars.find(char)
+		digit = (digit // mod) + (digit % mod)
+		total += digit
+		factor = 2 if factor == 1 else 1
+	if gstin[-1] != code_point_chars[((mod - (total % mod)) % mod)]:
+		frappe.throw(_("Invalid GSTIN! The check digit validation has failed. " +
+			"Please ensure you've typed the GSTIN correctly."))
 
 def get_itemised_tax_breakup_header(item_doctype, tax_accounts):
 	if frappe.get_meta(item_doctype).has_field('gst_hsn_code'):
diff --git a/erpnext/selling/doctype/customer/customer.py b/erpnext/selling/doctype/customer/customer.py
index b17345c2e75..2a6853aa67d 100644
--- a/erpnext/selling/doctype/customer/customer.py
+++ b/erpnext/selling/doctype/customer/customer.py
@@ -173,6 +173,11 @@ class Customer(TransactionBase):
 				frappe.throw(_("""New credit limit is less than current outstanding amount for the customer. Credit limit has to be atleast {0}""").format(outstanding_amt))
 
 	def on_trash(self):
+		if self.customer_primary_contact:
+			frappe.db.sql("""update `tabCustomer`
+				set customer_primary_contact=null, mobile_no=null, email_id=null
+				where name=%s""", self.name)
+
 		delete_contact_and_address('Customer', self.name)
 		if self.lead_name:
 			frappe.db.sql("update `tabLead` set status='Interested' where name=%s", self.lead_name)
diff --git a/erpnext/selling/doctype/customer/test_customer.py b/erpnext/selling/doctype/customer/test_customer.py
index 45546e348aa..123fd552c6d 100644
--- a/erpnext/selling/doctype/customer/test_customer.py
+++ b/erpnext/selling/doctype/customer/test_customer.py
@@ -96,6 +96,15 @@ class TestCustomer(unittest.TestCase):
 
 		so.save()
 
+	def test_delete_customer_contact(self):
+		customer = frappe.get_doc(
+			get_customer_dict('_Test Customer for delete')).insert(ignore_permissions=True)
+
+		customer.mobile_no = "8989889890"
+		customer.save()
+		self.assertTrue(customer.customer_primary_contact)
+		frappe.delete_doc('Customer', customer.name)
+
 	def test_disabled_customer(self):
 		make_test_records("Item")
 
diff --git a/erpnext/stock/doctype/purchase_receipt/test_purchase_receipt.py b/erpnext/stock/doctype/purchase_receipt/test_purchase_receipt.py
index 29caea156a4..1207c5d128e 100644
--- a/erpnext/stock/doctype/purchase_receipt/test_purchase_receipt.py
+++ b/erpnext/stock/doctype/purchase_receipt/test_purchase_receipt.py
@@ -325,7 +325,8 @@ def make_purchase_receipt(**args):
 		"conversion_factor": args.conversion_factor or 1.0,
 		"serial_no": args.serial_no,
 		"stock_uom": args.stock_uom or "_Test UOM",
-		"uom": args.uom or "_Test UOM"
+		"uom": args.uom or "_Test UOM",
+		"cost_center": "_Test Cost Center - _TC"
 	})
 
 	if not args.do_not_save: