diff --git a/src/astroseasons.h b/src/astroseasons.h
--- a/src/astroseasons.h
+++ b/src/astroseasons.h
@@ -44,7 +44,7 @@
 
    A very good description of the astronomical seasons can be read at the
    Wikipedia,
-     http://en.wikipedia.org/wiki/Seasons
+     https://en.wikipedia.org/wiki/Seasons
 
    Note that this class represents the "Astronomical Seasons" and not
    the traditional "Seasons" which vary widely by culture.
diff --git a/src/holidayregion.h b/src/holidayregion.h
--- a/src/holidayregion.h
+++ b/src/holidayregion.h
@@ -112,7 +112,7 @@
      * May be either just a country code ("US" = USA) or may include a regional
      * identifier ("US-CA" = California).  Returns "XX" if not a country.
      *
-     * See http://en.wikipedia.org/wiki/ISO_3166-2
+     * See https://en.wikipedia.org/wiki/ISO_3166-2
      *
      * @return the full region code of the file
      */
@@ -126,7 +126,7 @@
      * May be either just a country code ("US" = USA) or may include a regional
      * identifier ("US-CA" = California).  Returns "XX" if not a country.
      *
-     * See http://en.wikipedia.org/wiki/ISO_3166-2
+     * See https://en.wikipedia.org/wiki/ISO_3166-2
      *
      * @param regionCode The code for the Holiday Region.
      * @return the full region code of the file
diff --git a/src/lunarphase.h b/src/lunarphase.h
--- a/src/lunarphase.h
+++ b/src/lunarphase.h
@@ -48,7 +48,7 @@
    + "last quarter": the left 50% of the moon is visible.
 
    A very good description of the lunar phases can be read at the Wikipedia,
-     http://en.wikipedia.org/wiki/Lunar_phase
+     https://en.wikipedia.org/wiki/Lunar_phase
 
    Note that crescent and gibbous phases are not currently supported.
 */
diff --git a/src/parsers/qcalendarsystem.cpp b/src/parsers/qcalendarsystem.cpp
--- a/src/parsers/qcalendarsystem.cpp
+++ b/src/parsers/qcalendarsystem.cpp
@@ -398,7 +398,7 @@
     case QCalendarSystem::ROCCalendar:
     case QCalendarSystem::ThaiCalendar: {
         // Formula from The Calendar FAQ by Claus Tondering
-        // http://www.tondering.dk/claus/cal/node3.html#SECTION003161000000000000000
+        // https://www.tondering.dk/claus/calendar.html
         qint64 a = jd + 32044;
         qint64 b = ((4 * a) + 3) / 146097;
         qint64 c = a - ((146097 * b) / 4);
@@ -458,7 +458,7 @@
 
     case QCalendarSystem::JulianCalendar: {
         // Formula from The Calendar FAQ by Claus Tondering
-        // http://www.tondering.dk/claus/cal/node3.html#SECTION003161000000000000000
+        // https://www.tondering.dk/claus/calendar.html
         qint64 b = 0;
         qint64 c = jd + 32082;
         qint64 d = ((4 * c) + 3) / 1461;
@@ -509,7 +509,7 @@
     case QCalendarSystem::ROCCalendar:
     case QCalendarSystem::ThaiCalendar: {
         // Formula from The Calendar FAQ by Claus Tondering
-        // http://www.tondering.dk/claus/cal/node3.html#SECTION003161000000000000000
+        // https://www.tondering.dk/claus/calendar.html
         int a = (14 - month) / 12;
         year = year + 4800 - a;
         int m = month + (12 * a) - 3;
@@ -566,7 +566,7 @@
 
     case QCalendarSystem::JulianCalendar: {
         // Formula from The Calendar FAQ by Claus Tondering
-        // http://www.tondering.dk/claus/cal/node3.html#SECTION003161000000000000000
+        // https://www.tondering.dk/claus/calendar.html
         int a = (14 - month) / 12;
         year = year + 4800 - a;
         int m = month + (12 * a) - 3;
diff --git a/src/sunriseset.cpp b/src/sunriseset.cpp
--- a/src/sunriseset.cpp
+++ b/src/sunriseset.cpp
@@ -1,7 +1,7 @@
 /*
   This file is part of the kholidays library.
 
-  Adapted from the Javascript found at http://www.esrl.noaa.gov/gmd/grad/solcalc
+  Adapted from the Javascript found at https://www.esrl.noaa.gov/gmd/grad/solcalc
   which is in the public domain.
 
   Copyright (c) 2012 Allen Winter <winter@kde.org>
diff --git a/src/zodiac.h b/src/zodiac.h
--- a/src/zodiac.h
+++ b/src/zodiac.h
@@ -40,7 +40,7 @@
 
    A very good description of the Zodiac calendars can be read at the
    Wikipedia,
-     http://en.wikipedia.org/wiki/Zodiac
+     https://en.wikipedia.org/wiki/Zodiac
 
    Disclaimer: I am by no means a Zodiac expert.  I put together this software
    based on some quick scanning of documents I found on the WWW.  Feel free