diff --git a/libc/bionic/mbstate.cpp b/libc/bionic/mbstate.cpp
new file mode 100644
index 0000000..cb327d8
--- /dev/null
+++ b/libc/bionic/mbstate.cpp
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
+ * COPYRIGHT OWNER 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 "private/bionic_mbstate.h"
+
+#include <errno.h>
+
+__LIBC_HIDDEN__ size_t mbstate_bytes_so_far(const mbstate_t* ps) {
+  return
+    (ps->__seq[2] != 0) ? 3 :
+    (ps->__seq[1] != 0) ? 2 :
+    (ps->__seq[0] != 0) ? 1 : 0;
+}
+
+__LIBC_HIDDEN__ void mbstate_set_byte(mbstate_t* ps, int i, char byte) {
+  ps->__seq[i] = static_cast<uint8_t>(byte);
+}
+
+__LIBC_HIDDEN__ uint8_t mbstate_get_byte(const mbstate_t* ps, int n) {
+  return ps->__seq[n];
+}
+
+__LIBC_HIDDEN__ size_t reset_and_return_illegal(int _errno, mbstate_t* ps) {
+  errno = _errno;
+  *(reinterpret_cast<uint32_t*>(ps->__seq)) = 0;
+  return __MB_ERR_ILLEGAL_SEQUENCE;
+}
+
+__LIBC_HIDDEN__ size_t reset_and_return(int _return, mbstate_t* ps) {
+  *(reinterpret_cast<uint32_t*>(ps->__seq)) = 0;
+  return _return;
+}