diff --git a/lib/util/timegm.c b/lib/util/timegm.c
index d87c4eaad..968d829f4 100644
--- a/lib/util/timegm.c
+++ b/lib/util/timegm.c
@@ -88,6 +88,7 @@ sudo_timegm(struct tm *tm)
 {
     time_t result;
 
+    tm->tm_isdst = 0;
     result = mktime(tm);
     if (result != -1)
 	result += get_gmtoff(&result);