diff --git a/libc/include/utmp.h b/libc/include/utmp.h
index ffd3c92..d764227 100644
--- a/libc/include/utmp.h
+++ b/libc/include/utmp.h
@@ -36,9 +36,15 @@
 #define _PATH_WTMP      "/var/log/wtmp"
 #define _PATH_LASTLOG   "/var/log/lastlog"
 
-#define	UT_NAMESIZE	8
-#define	UT_LINESIZE	8
-#define	UT_HOSTSIZE	16
+#ifdef __LP64__
+#define UT_NAMESIZE 32
+#define UT_LINESIZE 32
+#define UT_HOSTSIZE 256
+#else
+#define UT_NAMESIZE 8
+#define UT_LINESIZE 8
+#define UT_HOSTSIZE 16
+#endif
 
 #define USER_PROCESS 7