diff --git a/lib/asn1/der_put.c b/lib/asn1/der_put.c
index b8101458a..0b276d1eb 100644
--- a/lib/asn1/der_put.c
+++ b/lib/asn1/der_put.c
@@ -433,7 +433,8 @@ _heim_time2generalizedtime (time_t t, heim_octet_string *s, int gtimep)
      if (s->data == NULL)
 	 return ENOMEM;
      s->length = len;
-     _der_gmtime(t, &tm);
+     if (_der_gmtime(t, &tm) == NULL)
+	 return ASN1_BAD_TIMEFORMAT;
      if (gtimep)
 	 snprintf (s->data, len + 1, "%04d%02d%02d%02d%02d%02dZ",
 		   tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,