diff --git a/lib/libc/stdio/stdio.c b/lib/libc/stdio/stdio.c
index 4bee60804d4..c0860ebaded 100644
--- a/lib/libc/stdio/stdio.c
+++ b/lib/libc/stdio/stdio.c
@@ -164,6 +164,11 @@ _sseek(fp, offset, whence)
 	errret = errno;
 	if (errno == 0)
 		errno = serrno;
+
+	if (errret == 0 && (offset != 0 || whence != SEEK_CUR))
+		/* Disallow fseek() optimization inside read buffer */
+		fp->_flags |= __SMOD;
+
 	/*
 	 * Disallow negative seeks per POSIX.
 	 * It is needed here to help upper level caller