diff --git a/tests/test_mailgun_backend.py b/tests/test_mailgun_backend.py
index 8450942..38ceafe 100644
--- a/tests/test_mailgun_backend.py
+++ b/tests/test_mailgun_backend.py
@@ -146,7 +146,7 @@ class MailgunBackendStandardEmailTests(MailgunBackendMockAPITestCase):
 
     def test_unicode_attachment_correctly_decoded(self):
         # Slight modification from the Django unicode docs:
-        # http://django.readthedocs.org/en/latest/ref/unicode.html#email
+        # https://django.readthedocs.io/en/latest/ref/unicode.html#email
         self.message.attach("Une pièce jointe.html", '<p>\u2019</p>', mimetype='text/html')
         self.message.send()
         files = self.get_api_call_files()
diff --git a/tests/test_mandrill_backend.py b/tests/test_mandrill_backend.py
index 2c02297..4c7a711 100644
--- a/tests/test_mandrill_backend.py
+++ b/tests/test_mandrill_backend.py
@@ -172,7 +172,7 @@ class MandrillBackendStandardEmailTests(MandrillBackendMockAPITestCase):
 
     def test_unicode_attachment_correctly_decoded(self):
         # Slight modification from the Django unicode docs:
-        # http://django.readthedocs.org/en/latest/ref/unicode.html#email
+        # https://django.readthedocs.io/en/latest/ref/unicode.html#email
         self.message.attach("Une pièce jointe.html", '<p>\u2019</p>', mimetype='text/html')
         self.message.send()
         data = self.get_api_call_json()
diff --git a/tests/test_postmark_backend.py b/tests/test_postmark_backend.py
index a627bf3..a556fa2 100644
--- a/tests/test_postmark_backend.py
+++ b/tests/test_postmark_backend.py
@@ -173,7 +173,7 @@ class PostmarkBackendStandardEmailTests(PostmarkBackendMockAPITestCase):
 
     def test_unicode_attachment_correctly_decoded(self):
         # Slight modification from the Django unicode docs:
-        # http://django.readthedocs.org/en/latest/ref/unicode.html#email
+        # https://django.readthedocs.io/en/latest/ref/unicode.html#email
         self.message.attach("Une pièce jointe.html", '<p>\u2019</p>', mimetype='text/html')
         self.message.send()
         data = self.get_api_call_json()
diff --git a/tests/test_sendgrid_backend.py b/tests/test_sendgrid_backend.py
index a9e5fe7..f0b7765 100644
--- a/tests/test_sendgrid_backend.py
+++ b/tests/test_sendgrid_backend.py
@@ -221,7 +221,7 @@ class SendGridBackendStandardEmailTests(SendGridBackendMockAPITestCase):
 
     def test_unicode_attachment_correctly_decoded(self):
         # Slight modification from the Django unicode docs:
-        # http://django.readthedocs.org/en/latest/ref/unicode.html#email
+        # https://django.readthedocs.io/en/latest/ref/unicode.html#email
         self.message.attach("Une pièce jointe.html", '<p>\u2019</p>', mimetype='text/html')
         self.message.send()
         files = self.get_api_call_files()