diff --git a/CMakeLists.txt b/CMakeLists.txt
index ef97de14..ecb90a23 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,7 +27,7 @@ cmake_minimum_required(VERSION 3.0)
 project(nghttp2 VERSION 1.45.90)
 
 # See versioning rule:
-#  http://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
+#  https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
 set(LT_CURRENT  35)
 set(LT_REVISION 0)
 set(LT_AGE      21)
diff --git a/configure.ac b/configure.ac
index e7654ec3..7b7465d2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -22,7 +22,7 @@ dnl OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 dnl WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 dnl Do not change user variables!
-dnl http://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
+dnl https://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
 
 AC_PREREQ(2.61)
 AC_INIT([nghttp2], [1.46.0-DEV], [t-tujikawa@users.sourceforge.net])