diff --git a/libc/stdio/ungetc.c b/libc/stdio/ungetc.c
new file mode 100644
index 0000000..fe05258
--- /dev/null
+++ b/libc/stdio/ungetc.c
@@ -0,0 +1,141 @@
+/*	$OpenBSD: ungetc.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 <stdlib.h>
+#include <string.h>
+#include "local.h"
+
+static int __submore(FILE *);
+/*
+ * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
+ * the buffer moves, so that it points the same distance from the end,
+ * and move the bytes in the buffer around as necessary so that they
+ * are all at the end (stack-style).
+ */
+static int
+__submore(FILE *fp)
+{
+	int i;
+	unsigned char *p;
+
+	if (_UB(fp)._base == fp->_ubuf) {
+		/*
+		 * Get a new buffer (rather than expanding the old one).
+		 */
+		if ((p = malloc((size_t)BUFSIZ)) == NULL)
+			return (EOF);
+		_UB(fp)._base = p;
+		_UB(fp)._size = BUFSIZ;
+		p += BUFSIZ - sizeof(fp->_ubuf);
+		for (i = sizeof(fp->_ubuf); --i >= 0;)
+			p[i] = fp->_ubuf[i];
+		fp->_p = p;
+		return (0);
+	}
+	i = _UB(fp)._size;
+	p = realloc(_UB(fp)._base, i << 1);
+	if (p == NULL)
+		return (EOF);
+	/* no overlap (hence can use memcpy) because we doubled the size */
+	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
+	fp->_p = p + i;
+	_UB(fp)._base = p;
+	_UB(fp)._size = i << 1;
+	return (0);
+}
+
+int
+ungetc(int c, FILE *fp)
+{
+	if (c == EOF)
+		return (EOF);
+	if (!__sdidinit)
+		__sinit();
+	_SET_ORIENTATION(fp, -1);
+	if ((fp->_flags & __SRD) == 0) {
+		/*
+		 * Not already reading: no good unless reading-and-writing.
+		 * Otherwise, flush any current write stuff.
+		 */
+		if ((fp->_flags & __SRW) == 0)
+			return (EOF);
+		if (fp->_flags & __SWR) {
+			if (__sflush(fp))
+				return (EOF);
+			fp->_flags &= ~__SWR;
+			fp->_w = 0;
+			fp->_lbfsize = 0;
+		}
+		fp->_flags |= __SRD;
+	}
+	c = (unsigned char)c;
+
+	/*
+	 * If we are in the middle of ungetc'ing, just continue.
+	 * This may require expanding the current ungetc buffer.
+	 */
+	if (HASUB(fp)) {
+		if (fp->_r >= _UB(fp)._size && __submore(fp))
+			return (EOF);
+		*--fp->_p = c;
+		fp->_r++;
+		return (c);
+	}
+	fp->_flags &= ~__SEOF;
+
+	/*
+	 * If we can handle this by simply backing up, do so,
+	 * but never replace the original character.
+	 * (This makes sscanf() work when scanning `const' data.)
+	 */
+	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
+	    fp->_p[-1] == c) {
+		fp->_p--;
+		fp->_r++;
+		return (c);
+	}
+
+	/*
+	 * Create an ungetc buffer.
+	 * Initially, we will use the `reserve' buffer.
+	 */
+	fp->_ur = fp->_r;
+	fp->_up = fp->_p;
+	_UB(fp)._base = fp->_ubuf;
+	_UB(fp)._size = sizeof(fp->_ubuf);
+	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
+	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
+	fp->_r = 1;
+	return (c);
+}