diff -up shadow-4.1.0/src/groupmems.c.segfault shadow-4.1.0/src/groupmems.c
--- shadow-4.1.0/src/groupmems.c.segfault	2008-02-19 12:39:23.000000000 +0100
+++ shadow-4.1.0/src/groupmems.c	2008-02-19 12:55:06.000000000 +0100
@@ -106,7 +106,7 @@ static void addtogroup (char *user, char
 		}
 	}
 
-	members = (char **) realloc (members, sizeof (char *) * i);
+	members = (char **) realloc (members, sizeof (char *) * (i + 2));
 	members[i] = user;
 	members[i + 1] = NULL;
 }