diff --git a/include/common/standard.h b/include/common/standard.h
index 0a956e069..7af9c25ce 100644
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -1072,7 +1072,7 @@ extern const char *monthname[];
  * without using sprintf. return a pointer to the last char written (\0) or
  * NULL if there isn't enough space.
  */
-char *date2str_log(char *dest, struct tm *tm, struct timeval *date, size_t size);
+char *date2str_log(char *dest, const struct tm *tm, const struct timeval *date, size_t size);
 
 /* Return the GMT offset for a specific local time.
  * Both t and tm must represent the same time.
diff --git a/src/standard.c b/src/standard.c
index 732932ea1..04df94ead 100644
--- a/src/standard.c
+++ b/src/standard.c
@@ -2801,7 +2801,7 @@ const char *monthname[12] = {
  * without using sprintf. return a pointer to the last char written (\0) or
  * NULL if there isn't enough space.
  */
-char *date2str_log(char *dst, struct tm *tm, struct timeval *date, size_t size)
+char *date2str_log(char *dst, const struct tm *tm, const struct timeval *date, size_t size)
 {
 
 	if (size < 25) /* the size is fixed: 24 chars + \0 */