diff -ruN shadow-4.2/src/usermod.c shadow-4.2-mod/src/usermod.c
--- shadow-4.2/src/usermod.c	2017-01-04 13:56:58.000000000 +0100
+++ shadow-4.2-mod/src/usermod.c	2017-01-04 13:54:56.897842294 +0100
@@ -1593,6 +1593,11 @@
 		 * group entries.
 		 */
 		if (gr_lock () == 0) {
+			if (try_extrausers) {
+				gr_setdbname (EXTRAUSERS_GROUP_FILE);
+				open_files ();
+				return;
+			}
 			fprintf (stderr,
 			         _("%s: cannot lock %s; try again later.\n"),
 			         Prog, gr_dbname ());
@@ -1600,6 +1605,13 @@
 		}
 		gr_locked = true;
 		if (gr_open (O_RDWR) == 0) {
+			if (try_extrausers) {
+				gr_unlock ();
+				gr_locked ();
+				gr_setdbname (EXTRAUSERS_GROUP_FILE);
+				open_files ();
+				return;
+			}
 			fprintf (stderr,
 			         _("%s: cannot open %s\n"),
 			         Prog, gr_dbname ());
@@ -1607,6 +1619,15 @@
 		}
 #ifdef SHADOWGRP
 		if (is_shadow_grp && (sgr_lock () == 0)) {
+			if (try_extrausers) {
+				gr_close ();
+				gr_unlock ();
+				gr_locked = false;
+				gr_setdbname (EXTRAUSERS_GROUP_FILE);
+				sgr_setdbname (EXTRAUSERS_SHADOWGROUP_FILE);
+				open_files ();
+				return;
+			}
 			fprintf (stderr,
 			         _("%s: cannot lock %s; try again later.\n"),
 			         Prog, sgr_dbname ());
@@ -1614,6 +1635,17 @@
 		}
 		sgr_locked = true;
 		if (is_shadow_grp && (sgr_open (O_RDWR) == 0)) {
+			if (try_extrausers) {
+				gr_close ();
+				gr_unlock ();
+				sgr_unlock ();
+				gr_locked = false;
+				sgr_locked = false;
+				gr_setdbname (EXTRAUSERS_GROUP_FILE);
+				sgr_setdbname (EXTRAUSERS_SHADOWGROUP_FILE);
+				open_files ();
+				return;
+			}
 			fprintf (stderr,
 			         _("%s: cannot open %s\n"),
 			         Prog, sgr_dbname ());