diff --git a/libc/stdio/wbuf.c b/libc/stdio/wbuf.c
new file mode 100644
index 0000000..c757799
--- /dev/null
+++ b/libc/stdio/wbuf.c
@@ -0,0 +1,84 @@
+/*	$OpenBSD: wbuf.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */
+/*-
+ * Copyright (c) 1990, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Chris Torek.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include "local.h"
+
+/*
+ * Write the given character into the (probably full) buffer for
+ * the given file.  Flush the buffer out if it is or becomes full,
+ * or if c=='\n' and the file is line buffered.
+ */
+int
+__swbuf(int c, FILE *fp)
+{
+	int n;
+
+	_SET_ORIENTATION(fp, -1);
+	/*
+	 * In case we cannot write, or longjmp takes us out early,
+	 * make sure _w is 0 (if fully- or un-buffered) or -_bf._size
+	 * (if line buffered) so that we will get called again.
+	 * If we did not do this, a sufficient number of putc()
+	 * calls might wrap _w from negative to positive.
+	 */
+	fp->_w = fp->_lbfsize;
+	if (cantwrite(fp)) {
+		errno = EBADF;
+		return (EOF);
+	}
+	c = (unsigned char)c;
+
+	/*
+	 * If it is completely full, flush it out.  Then, in any case,
+	 * stuff c into the buffer.  If this causes the buffer to fill
+	 * completely, or if c is '\n' and the file is line buffered,
+	 * flush it (perhaps a second time).  The second flush will always
+	 * happen on unbuffered streams, where _bf._size==1; fflush()
+	 * guarantees that putc() will always call wbuf() by setting _w
+	 * to 0, so we need not do anything else.
+	 */
+	n = fp->_p - fp->_bf._base;
+	if (n >= fp->_bf._size) {
+		if (fflush(fp))
+			return (EOF);
+		n = 0;
+	}
+	fp->_w--;
+	*fp->_p++ = c;
+	if (++n == fp->_bf._size || (fp->_flags & __SLBF && c == '\n'))
+		if (fflush(fp))
+			return (EOF);
+	return (c);
+}