diff --git a/libc/include/bits/bionic_multibyte_result.h b/libc/include/bits/bionic_multibyte_result.h
new file mode 100644
index 0000000..0d5cf21
--- /dev/null
+++ b/libc/include/bits/bionic_multibyte_result.h
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2023 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.
+ */
+
+#pragma once
+
+/**
+ * @file bits/bionic_multibyte_result.h
+ * @brief Named values for the magic number return values of multibyte
+ * conversion APIs defined by C.
+ */
+
+#include <stddef.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/**
+ * @brief The error values defined by C for multibyte conversion APIs.
+ *
+ * Refer to C23 7.30.1 Restartable multibyte/wide character conversion functions
+ * for more details.
+ */
+enum : size_t {
+  /// @brief An encoding error occurred. The bytes read are not a valid unicode
+  /// character, nor are they a partially valid character.
+  BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE = -1UL,
+#define BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE
+
+  /// @brief The bytes read may produce a valid unicode character, but the
+  /// sequence is incomplete. Future calls may complete the character.
+  BIONIC_MULTIBYTE_RESULT_INCOMPLETE_SEQUENCE = -2UL,
+#define BIONIC_MULTIBYTE_RESULT_INCOMPLETE_SEQUENCE BIONIC_MULTIBYTE_RESULT_INCOMPLETE_SEQUENCE
+
+  /// @brief The output of the call was the result of a previous successful
+  /// decoding. No new bytes were consumed.
+  ///
+  /// The common case for this return value is when mbrtoc16 returns the low
+  /// surrogate of a pair.
+  BIONIC_MULTIBYTE_RESULT_NO_BYTES_CONSUMED = -3UL,
+#define BIONIC_MULTIBYTE_RESULT_NO_BYTES_CONSUMED BIONIC_MULTIBYTE_RESULT_NO_BYTES_CONSUMED
+};
+
+__END_DECLS
diff --git a/libc/include/uchar.h b/libc/include/uchar.h
index 0c7424d..626372a 100644
--- a/libc/include/uchar.h
+++ b/libc/include/uchar.h
@@ -35,6 +35,8 @@
 
 #include <stddef.h>
 #include <sys/cdefs.h>
+
+#include <bits/bionic_multibyte_result.h>
 #include <bits/mbstate_t.h>
 
 __BEGIN_DECLS
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 2671580..c4e9679 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -37,6 +37,7 @@
 #include <time.h>
 #include <xlocale.h>
 
+#include <bits/bionic_multibyte_result.h>
 #include <bits/mbstate_t.h>
 #include <bits/wchar_limits.h>
 #include <bits/wctype.h>