diff --git a/linkcheck/checker/fileurl.py b/linkcheck/checker/fileurl.py
index a5d36ecf..6e0753e2 100644
--- a/linkcheck/checker/fileurl.py
+++ b/linkcheck/checker/fileurl.py
@@ -71,7 +71,7 @@ def get_os_filename(path):
         path = prepare_urlpath_for_nt(path)
     res = urllib.request.url2pathname(fileutil.path_safe(path))
     if os.name == 'nt' and res.endswith(':') and len(res) == 2:
-        # Work around http://bugs.python.org/issue11474
+        # Work around https://bugs.python.org/issue11474
         res += os.sep
     return res
 
diff --git a/linkcheck/checker/mailtourl.py b/linkcheck/checker/mailtourl.py
index 5f358c13..fd527f2e 100644
--- a/linkcheck/checker/mailtourl.py
+++ b/linkcheck/checker/mailtourl.py
@@ -137,20 +137,20 @@ class MailtoUrl(urlbase.UrlBase):
     def check_email_syntax(self, mail):
         """Check email syntax. The relevant RFCs:
         - How to check names (memo):
-          http://tools.ietf.org/html/rfc3696
+          https://tools.ietf.org/html/rfc3696
         - Email address syntax
-          http://tools.ietf.org/html/rfc2822
+          https://tools.ietf.org/html/rfc2822
         - SMTP protocol
-          http://tools.ietf.org/html/rfc5321#section-4.1.3
+          https://tools.ietf.org/html/rfc5321#section-4.1.3
         - IPv6
-          http://tools.ietf.org/html/rfc4291#section-2.2
+          https://tools.ietf.org/html/rfc4291#section-2.2
         - Host syntax
-          http://tools.ietf.org/html/rfc1123#section-2
+          https://tools.ietf.org/html/rfc1123#section-2
         """
         # length checks
 
         # restrict email length to 256 characters
-        # http://www.rfc-editor.org/errata_search.php?eid=1003
+        # https://www.rfc-editor.org/errata_search.php?eid=1003
         if len(mail) > 256:
             self.set_result(
                 _(
@@ -210,7 +210,7 @@ class MailtoUrl(urlbase.UrlBase):
 
         # local part syntax check
 
-        # Rules taken from http://tools.ietf.org/html/rfc3696#section-3
+        # Rules taken from https://tools.ietf.org/html/rfc3696#section-3
         if is_quoted(local):
             if is_missing_quote(local):
                 self.set_result(
diff --git a/linkcheck/logger/dot.py b/linkcheck/logger/dot.py
index 04059bcf..fb17d0a1 100644
--- a/linkcheck/logger/dot.py
+++ b/linkcheck/logger/dot.py
@@ -15,7 +15,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 """
 A DOT graph format logger. The specification has been taken from
-http://www.graphviz.org/doc/info/lang.html
+https://www.graphviz.org/doc/info/lang.html
 """
 from .graph import _GraphLogger
 
diff --git a/linkcheck/logger/sitemapxml.py b/linkcheck/logger/sitemapxml.py
index 7f3b16c2..827a3c67 100644
--- a/linkcheck/logger/sitemapxml.py
+++ b/linkcheck/logger/sitemapxml.py
@@ -34,7 +34,7 @@ HTML_TYPES = ('text/html', "application/xhtml+xml")
 
 
 class SitemapXmlLogger(xmllog._XMLLogger):
-    """Sitemap XML output according to http://www.sitemaps.org/protocol.html
+    """Sitemap XML output according to https://www.sitemaps.org/protocol.html
     """
 
     LoggerName = 'sitemap'