diff --git a/libc/stdio/vsnprintf.c b/libc/stdio/vsnprintf.c
new file mode 100644
index 0000000..e6dd009
--- /dev/null
+++ b/libc/stdio/vsnprintf.c
@@ -0,0 +1,64 @@
+/*	$OpenBSD: vsnprintf.c,v 1.12 2006/01/06 18:53:04 millert 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 <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include "local.h"
+
+int
+vsnprintf(char *str, size_t n, const char *fmt, __va_list ap)
+{
+	int ret;
+	char dummy;
+	FILE f;
+	struct __sfileext fext;
+
+	_FILEEXT_SETUP(&f, &fext);
+
+	/* While snprintf(3) specifies size_t stdio uses an int internally */
+	if (n > INT_MAX)
+		n = INT_MAX;
+	/* Stdio internals do not deal correctly with zero length buffer */
+	if (n == 0) {
+		str = &dummy;
+		n = 1;
+	}
+	f._file = -1;
+	f._flags = __SWR | __SSTR;
+	f._bf._base = f._p = (unsigned char *)str;
+	f._bf._size = f._w = n - 1;
+	ret = vfprintf(&f, fmt, ap);
+	*f._p = '\0';
+	return (ret);
+}