diff -up shadow-4.1.2/src/groupmems.c.gmNoGroup shadow-4.1.2/src/groupmems.c
--- shadow-4.1.2/src/groupmems.c.gmNoGroup	2008-09-24 15:00:30.000000000 +0200
+++ shadow-4.1.2/src/groupmems.c	2008-09-24 15:07:20.000000000 +0200
@@ -56,6 +56,7 @@
 #define EXIT_NOT_MEMBER		6	/* member of group does not exist */
 #define EXIT_MEMBER_EXISTS	7	/* member of group already exists */
 #define E_BAD_ARG		8       /* invalid argument to option */
+#define EXIT_NOT_GROUP		8	/* group does not exist */
 
 #define TRUE 1
 #define FALSE 0
@@ -293,6 +294,10 @@ int main (int argc, char **argv) 
 	}
 
 	grp = (struct group *) gr_locate (name);
+	if (NULL == grp) {
+		fputs (_("Specified group does not exist\n"), stderr);
+		exit (EXIT_NOT_GROUP);
+	}
 
 	if (NULL != adduser) {
 		grp->gr_mem = addtogroup (adduser, grp->gr_mem);