diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index 22467a211df..e051961712e 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -444,7 +444,7 @@ struct __nl_cat_d;
 struct _xlocale;
 struct __nl_cat_d *__catopen_l(const char *name, int type,
 	    struct _xlocale *locale);
-int __strerror_rl(int errnum, char *strerrbuf, size_t buflen,
+int __strerror_rl(int errnum, char *strerrbuf, __size_t buflen,
 	    struct _xlocale *locale);
 
 #endif /* _LIBC_PRIVATE_H_ */