diff -up shadow-4.11.1/src/chage.c.null-tm shadow-4.11.1/src/chage.c
diff -up shadow-4.11.1/src/lastlog.c.null-tm shadow-4.11.1/src/lastlog.c
--- shadow-4.11.1/src/lastlog.c.null-tm	2022-01-03 15:31:56.348555620 +0100
+++ shadow-4.11.1/src/lastlog.c	2022-01-03 15:38:41.262229024 +0100
@@ -151,9 +151,12 @@ static void print_one (/*@null@*/const s
 
 	ll_time = ll.ll_time;
 	tm = localtime (&ll_time);
-	strftime (ptime, sizeof (ptime), "%a %b %e %H:%M:%S %z %Y", tm);
-	cp = ptime;
-
+	if (tm == NULL) {
+		cp = "(unknown)";
+	} else {
+		strftime (ptime, sizeof (ptime), "%a %b %e %H:%M:%S %z %Y", tm);
+		cp = ptime;
+	}
 	if (ll.ll_time == (time_t) 0) {
 		cp = _("**Never logged in**\0");
 	}
diff -up shadow-4.11.1/src/passwd.c.null-tm shadow-4.11.1/src/passwd.c
diff -up shadow-4.11.1/src/usermod.c.null-tm shadow-4.11.1/src/usermod.c