diff -up shadow-4.8/src/useradd.c.invalid-shell shadow-4.8/src/useradd.c
--- shadow-4.8/src/useradd.c.invalid-shell	2020-01-16 08:47:13.841921106 +0100
+++ shadow-4.8/src/useradd.c	2020-01-16 08:57:26.338421901 +0100
@@ -1277,15 +1277,22 @@ static void process_flags (int argc, cha
 				if (   ( !VALID (optarg) )
 				    || (   ('\0' != optarg[0])
 				        && ('/'  != optarg[0])
-				        && ('*'  != optarg[0]) )
-				    || (stat(optarg, &st) != 0)
-				    || (S_ISDIR(st.st_mode))
-				    || (access(optarg, X_OK) != 0)) {
+				        && ('*'  != optarg[0]) )) {
 					fprintf (stderr,
 					         _("%s: invalid shell '%s'\n"),
 					         Prog, optarg);
 					exit (E_BAD_ARG);
 				}
+				if (    '\0' != optarg[0]
+				     && '*'  != optarg[0]
+				     && strcmp(optarg, "/sbin/nologin") != 0
+				     && (   stat(optarg, &st) != 0
+				         || S_ISDIR(st.st_mode)
+				         || access(optarg, X_OK) != 0)) {
+					fprintf (stderr,
+					         _("%s: Warning: missing or non-executable shell '%s'\n"),
+					         Prog, optarg);
+				}
 				user_shell = optarg;
 				def_shell = optarg;
 				sflg = true;