diff -up shadow-4.1.5.1/lib/defines.h.long-entry shadow-4.1.5.1/lib/defines.h
--- shadow-4.1.5.1/lib/defines.h.long-entry	2011-09-18 22:44:10.000000000 +0200
+++ shadow-4.1.5.1/lib/defines.h	2018-04-24 16:34:31.261417493 +0200
@@ -382,4 +382,7 @@ extern char *strerror ();
 # endif
 #endif
 
+/* Maximum length of passwd entry */
+#define PASSWD_ENTRY_MAX_LENGTH 32768
+
 #endif				/* _DEFINES_H_ */
diff -up shadow-4.1.5.1/lib/pwio.c.long-entry shadow-4.1.5.1/lib/pwio.c
--- shadow-4.1.5.1/lib/pwio.c.long-entry	2011-02-16 21:32:24.000000000 +0100
+++ shadow-4.1.5.1/lib/pwio.c	2018-04-24 16:34:31.263417454 +0200
@@ -79,7 +79,10 @@ static int passwd_put (const void *ent,
 	    || (pw->pw_gid == (gid_t)-1)
 	    || (valid_field (pw->pw_gecos, ":\n") == -1)
 	    || (valid_field (pw->pw_dir, ":\n") == -1)
-	    || (valid_field (pw->pw_shell, ":\n") == -1)) {
+	    || (valid_field (pw->pw_shell, ":\n") == -1)
+	    || (strlen (pw->pw_name) + strlen (pw->pw_passwd) +
+	        strlen (pw->pw_gecos) + strlen (pw->pw_dir) +
+	        strlen (pw->pw_shell) + 100 > PASSWD_ENTRY_MAX_LENGTH)) {
 		return -1;
 	}
 
diff -up shadow-4.1.5.1/lib/sgetpwent.c.long-entry shadow-4.1.5.1/lib/sgetpwent.c
--- shadow-4.1.5.1/lib/sgetpwent.c.long-entry	2009-04-06 06:28:53.000000000 +0200
+++ shadow-4.1.5.1/lib/sgetpwent.c	2018-04-24 16:34:31.263417454 +0200
@@ -57,7 +57,7 @@
 struct passwd *sgetpwent (const char *buf)
 {
 	static struct passwd pwent;
-	static char pwdbuf[1024];
+	static char pwdbuf[PASSWD_ENTRY_MAX_LENGTH];
 	register int i;
 	register char *cp;
 	char *fields[NFIELDS];
@@ -67,8 +67,10 @@ struct passwd *sgetpwent (const char *bu
 	 * the password structure remain valid.
 	 */
 
-	if (strlen (buf) >= sizeof pwdbuf)
+	if (strlen (buf) >= sizeof pwdbuf) {
+		fprintf (stderr, "Too long passwd entry encountered, file corruption?\n");
 		return 0;	/* fail if too long */
+	}
 	strcpy (pwdbuf, buf);
 
 	/*
diff -up shadow-4.1.5.1/lib/sgetspent.c.long-entry shadow-4.1.5.1/lib/sgetspent.c
--- shadow-4.1.5.1/lib/sgetspent.c.long-entry	2009-04-12 04:46:43.000000000 +0200
+++ shadow-4.1.5.1/lib/sgetspent.c	2018-04-24 16:34:31.264417435 +0200
@@ -48,7 +48,7 @@
  */
 struct spwd *sgetspent (const char *string)
 {
-	static char spwbuf[1024];
+	static char spwbuf[PASSWD_ENTRY_MAX_LENGTH];
 	static struct spwd spwd;
 	char *fields[FIELDS];
 	char *cp;
@@ -61,6 +61,7 @@ struct spwd *sgetspent (const char *stri
 	 */
 
 	if (strlen (string) >= sizeof spwbuf) {
+		fprintf (stderr, "Too long shadow entry encountered, file corruption?\n");
 		return 0;	/* fail if too long */
 	}
 	strcpy (spwbuf, string);
diff -up shadow-4.1.5.1/lib/shadowio.c.long-entry shadow-4.1.5.1/lib/shadowio.c
--- shadow-4.1.5.1/lib/shadowio.c.long-entry	2011-02-16 21:32:24.000000000 +0100
+++ shadow-4.1.5.1/lib/shadowio.c	2018-04-24 16:34:31.265417416 +0200
@@ -78,7 +78,9 @@ static int shadow_put (const void *ent,
 
 	if (   (NULL == sp)
 	    || (valid_field (sp->sp_namp, ":\n") == -1)
-	    || (valid_field (sp->sp_pwdp, ":\n") == -1)) {
+	    || (valid_field (sp->sp_pwdp, ":\n") == -1)
+	    || (strlen (sp->sp_namp) + strlen (sp->sp_pwdp) +
+	        1000 > PASSWD_ENTRY_MAX_LENGTH)) {
 		return -1;
 	}