_PW_NAME_LEN doesn't include the NUL, MAXLOGNAME does.

src/include/pwd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: pwd.h,v 1.10 2001/01/31 17:42:25 deraadt Exp $	*/
+/*	$OpenBSD: pwd.h,v 1.11 2001/02/13 14:48:40 pjanzen Exp $	*/
 /*	$NetBSD: pwd.h,v 1.9 1996/05/15 21:36:45 jtc Exp $	*/
 
 /*-
@@ -66,8 +66,9 @@
 
 #define	_PASSWORD_EFMT1		'_'	/* extended encryption format */
 
-#define	_PASSWORD_LEN		128	/* max length, not counting NULL */
-#define	_PW_NAME_LEN		32	/* max length, not counting NULL */
+#define	_PASSWORD_LEN		128	/* max length, not counting NUL */
+#define	_PW_NAME_LEN		31	/* max length, not counting NUL */
+					/* Should be MAXLOGNAME - 1 */
 
 #define _PASSWORD_NOUID		0x01	/* flag for no specified uid. */
 #define _PASSWORD_NOGID		0x02	/* flag for no specified gid. */