diff --git a/expat/xmlwf/readfilemap.c b/expat/xmlwf/readfilemap.c
index 2cb53fee..6b562803 100644
--- a/expat/xmlwf/readfilemap.c
+++ b/expat/xmlwf/readfilemap.c
@@ -55,7 +55,7 @@
 #  define EXPAT_read_count_t int
 #  define EXPAT_read_req_t unsigned int
 #else /* POSIX */
-/* http://pubs.opengroup.org/onlinepubs/009695399/functions/read.html */
+/* https://pubs.opengroup.org/onlinepubs/009695399/functions/read.html */
 #  define EXPAT_read read
 #  define EXPAT_read_count_t ssize_t
 #  define EXPAT_read_req_t size_t