diff --git a/libc/stdio/wsetup.c b/libc/stdio/wsetup.c
new file mode 100644
index 0000000..0834223
--- /dev/null
+++ b/libc/stdio/wsetup.c
@@ -0,0 +1,86 @@
+/*	$OpenBSD: wsetup.c,v 1.7 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 <stdlib.h>
+#include "local.h"
+
+/*
+ * Various output routines call wsetup to be sure it is safe to write,
+ * because either _flags does not include __SWR, or _buf is NULL.
+ * _wsetup returns 0 if OK to write, nonzero otherwise.
+ */
+int
+__swsetup(FILE *fp)
+{
+	/* make sure stdio is set up */
+	if (!__sdidinit)
+		__sinit();
+
+	/*
+	 * If we are not writing, we had better be reading and writing.
+	 */
+	if ((fp->_flags & __SWR) == 0) {
+		if ((fp->_flags & __SRW) == 0)
+			return (EOF);
+		if (fp->_flags & __SRD) {
+			/* clobber any ungetc data */
+			if (HASUB(fp))
+				FREEUB(fp);
+			fp->_flags &= ~(__SRD|__SEOF);
+			fp->_r = 0;
+			fp->_p = fp->_bf._base;
+		}
+		fp->_flags |= __SWR;
+	}
+
+	/*
+	 * Make a buffer if necessary, then set _w.
+	 */
+	if (fp->_bf._base == NULL) {
+		if ((fp->_flags & (__SSTR | __SALC)) == __SSTR)
+			return (EOF);
+		__smakebuf(fp);
+	}
+	if (fp->_flags & __SLBF) {
+		/*
+		 * It is line buffered, so make _lbfsize be -_bufsize
+		 * for the putc() macro.  We will change _lbfsize back
+		 * to 0 whenever we turn off __SWR.
+		 */
+		fp->_w = 0;
+		fp->_lbfsize = -fp->_bf._size;
+	} else
+		fp->_w = fp->_flags & __SNBF ? 0 : fp->_bf._size;
+	return (0);
+}