diff --git a/configure.ac b/configure.ac
index 06487861..535a9dc2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -43,7 +43,7 @@ AM_INIT_AUTOMAKE([subdir-objects])
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
 dnl See versioning rule:
-dnl  http://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
+dnl  https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
 AC_SUBST(LT_CURRENT, 34)
 AC_SUBST(LT_REVISION, 2)
 AC_SUBST(LT_AGE, 20)