diff --git a/addons/mail/models/mail_thread.py b/addons/mail/models/mail_thread.py
index 8b9c9de72d4..28e25a259c8 100644
--- a/addons/mail/models/mail_thread.py
+++ b/addons/mail/models/mail_thread.py
@@ -1523,6 +1523,10 @@ class MailThread(models.AbstractModel):
                     part.set_charset('utf-8')
                 encoding = part.get_content_charset()  # None if attachment
 
+                # Correcting MIME type for PDF files
+                if part.get('Content-Type', '').startswith('pdf;'):
+                    part.replace_header('Content-Type', 'application/pdf' + part.get('Content-Type', '')[3:])
+
                 content = part.get_content()
                 info = {'encoding': encoding}
                 # 0) Inline Attachments -> attachments, with a third part in the tuple to match cid / attachment
diff --git a/addons/test_mail/data/test_mail_data.py b/addons/test_mail/data/test_mail_data.py
index c2e6fdb0454..6e6626a16a4 100644
--- a/addons/test_mail/data/test_mail_data.py
+++ b/addons/test_mail/data/test_mail_data.py
@@ -1292,3 +1292,23 @@ To: lucie@petitebedaine.fr
 From: "Bruce Wayne" <bruce@wayneenterprises.com>
 
 SSBhbSB0aGUgQmF0TWFuCg=="""
+
+MAIL_PDF_MIME_TEMPLATE = """\
+To: {to}
+From: {email_from}
+Subject: {subject}
+MIME-Version: 1.0
+Content-Type: multipart/alternative;
+    boundary="----=_Part_4200734_24778174.1344608186754"
+Date: Fri, 10 Aug 2012 14:16:26 +0000
+
+------=_Part_4200734_24778174.1344608186754
+Content-Type: {pdf_mime}; name="scan_soraya.lernout_1691652648.pdf"
+Content-Transfer-Encoding: base64
+
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
+
+------=_Part_4200734_24778174.1344608186754--
+"""
+
+PDF_PARSED = b'''%PDF-1.1\n%\xc2\xa5\xc2\xb1\xc3\xab\n\n1 0 obj\n  << /Type /Catalog\n     /Pages 2 0 R\n  >>\nendobj\n\n2 0 obj\n  << /Type /Pages\n     /Kids [3 0 R]\n     /Count 1\n     /MediaBox [0 0 300 144]\n  >>\nendobj\n\n3 0 obj\n  <<  /Type /Page\n      /Parent 2 0 R\n      /Resources\n       << /Font\n           << /F1\n               << /Type /Font\n                  /Subtype /Type1\n                  /BaseFont /Times-Roman\n               >>\n           >>\n       >>\n      /Contents 4 0 R\n  >>\nendobj\n\n4 0 obj\n  << /Length 55 >>\nstream\n  BT\n    /F1 18 Tf\n    0 0 Td\n    (Hello World) Tj\n  ET\nendstream\nendobj\n\nxref\n0 5\n0000000000 65535 f \n0000000018 00000 n \n0000000077 00000 n \n0000000178 00000 n \n0000000457 00000 n \ntrailer\n  <<  /Root 1 0 R\n      /Size 5\n  >>\nstartxref\n565\n%%EOF\n'''
diff --git a/addons/test_mail/tests/test_mail_gateway.py b/addons/test_mail/tests/test_mail_gateway.py
index c5fc9377ffe..35040c2b10b 100644
--- a/addons/test_mail/tests/test_mail_gateway.py
+++ b/addons/test_mail/tests/test_mail_gateway.py
@@ -83,6 +83,19 @@ class TestEmailParsing(MailCommon):
         res = self.env['mail.thread'].message_parse(self.from_string(test_mail_data.MAIL_MULTIPART_WEIRD_FILENAME))
         self.assertEqual(res['attachments'][0][0], '62_@;,][)=.(ÇÀÉ.txt')
 
+    def test_message_parse_attachment_pdf_nonstandard_mime(self):
+        # This test checks if aliasing content-type (mime type) of "pdf" with "application/pdf" works correctly. (i.e. Treat "pdf" as "application/pdf")
+
+        # Baseline check. Parsing mail with "application/pdf"
+        mail_with_standard_mime = self.format(test_mail_data.MAIL_PDF_MIME_TEMPLATE, pdf_mime="application/pdf")
+        res_std = self.env['mail.thread'].message_parse(self.from_string(mail_with_standard_mime))
+        self.assertEqual(res_std['attachments'][0].content, test_mail_data.PDF_PARSED, "Attachment with Content-Type: application/pdf must parse without error")
+
+        # Parsing the same email, but with content-type set to "pdf"
+        mail_with_aliased_mime = self.format(test_mail_data.MAIL_PDF_MIME_TEMPLATE, pdf_mime="pdf")
+        res_alias = self.env['mail.thread'].message_parse(self.from_string(mail_with_aliased_mime))
+        self.assertEqual(res_alias['attachments'][0].content, test_mail_data.PDF_PARSED, "Attachment with aliased Content-Type: pdf must parse without error")
+
     def test_message_parse_bugs(self):
         """ Various corner cases or message parsing """
         # message without Final-Recipient