diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index fd653d9..268db78 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -73,9 +73,9 @@
 #define	__SMBF	0x0080		/* _buf is from malloc */
 #define	__SAPP	0x0100		/* fdopen()ed in append mode */
 #define	__SSTR	0x0200		/* this is an sprintf/snprintf string */
-#define	__SOPT	0x0400		/* do fseek() optimization */
-#define	__SNPT	0x0800		/* do not do fseek() optimization */
-#define	__SOFF	0x1000		/* set iff _offset is in fact correct */
+/* #define __SOPT 0x0400 --- historical (do fseek() optimization). */
+/* #define __SNPT 0x0800 --- historical (do not do fseek() optimization). */
+/* #define __SOFF 0x1000 --- historical (set iff _offset is in fact correct). */
 #define	__SMOD	0x2000		/* true => fgetln modified _p text */
 #define	__SALC	0x4000		/* allocate string space dynamically */
 #define	__SIGN	0x8000		/* ignore this file in _fwalk */