diff --git a/src/timezone/localtime.c b/src/timezone/localtime.c
index d004e5e..05877e1 100644
--- a/src/timezone/localtime.c
+++ b/src/timezone/localtime.c
@@ -1244,7 +1244,7 @@ localsub(struct state const * sp, pg_time_t const * timep,
 	if (result)
 	{
 		result->tm_isdst = ttisp->tt_isdst;
-		result->tm_zone = (char *) &sp->chars[ttisp->tt_abbrind];
+		result->tm_zone = (const char *) &sp->chars[ttisp->tt_abbrind];
 	}
 	return result;
 }