Index: shadow-4.5/src/chage.c
===================================================================
--- shadow-4.5.orig/src/chage.c
+++ shadow-4.5/src/chage.c
@@ -168,6 +168,10 @@ static void date_to_str (char *buf, size
 	struct tm *tp;
 
 	tp = gmtime (&date);
+	if (tp == NULL) {
+		(void) snprintf (buf, maxsize, "(unknown)");
+		return;
+	}
 #ifdef HAVE_STRFTIME
 	(void) strftime (buf, maxsize, "%Y-%m-%d", tp);
 #else
Index: shadow-4.5/src/lastlog.c
===================================================================
--- shadow-4.5.orig/src/lastlog.c
+++ shadow-4.5/src/lastlog.c
@@ -158,13 +158,17 @@ static void print_one (/*@null@*/const s
 
 	ll_time = ll.ll_time;
 	tm = localtime (&ll_time);
+	if (tm == NULL) {
+		cp = "(unknown)";
+	} else {
 #ifdef HAVE_STRFTIME
-	strftime (ptime, sizeof (ptime), "%a %b %e %H:%M:%S %z %Y", tm);
-	cp = ptime;
+		strftime (ptime, sizeof (ptime), "%a %b %e %H:%M:%S %z %Y", tm);
+		cp = ptime;
 #else
-	cp = asctime (tm);
-	cp[24] = '\0';
+		cp = asctime (tm);
+		cp[24] = '\0';
 #endif
+	}
 
 	if (ll.ll_time == (time_t) 0) {
 		cp = _("**Never logged in**\0");
Index: shadow-4.5/src/passwd.c
===================================================================
--- shadow-4.5.orig/src/passwd.c
+++ shadow-4.5/src/passwd.c
@@ -455,6 +455,9 @@ static /*@observer@*/const char *date_to
 	struct tm *tm;
 
 	tm = gmtime (&t);
+	if (tm == NULL) {
+		return "(unknown)";
+	}
 #ifdef HAVE_STRFTIME
 	(void) strftime (buf, sizeof buf, "%m/%d/%Y", tm);
 #else				/* !HAVE_STRFTIME */
Index: shadow-4.5/src/usermod.c
===================================================================
--- shadow-4.5.orig/src/usermod.c
+++ shadow-4.5/src/usermod.c
@@ -210,6 +210,10 @@ static void date_to_str (/*@unique@*//*@
 	} else {
 		time_t t = (time_t) date;
 		tp = gmtime (&t);
+		if (tp == NULL) {
+			strncpy (buf, "unknown", maxsize);
+			return;
+		}
 #ifdef HAVE_STRFTIME
 		strftime (buf, maxsize, "%Y-%m-%d", tp);
 #else