diff --git a/libc/hdr/types/CMakeLists.txt b/libc/hdr/types/CMakeLists.txt
index 1ef1a2bee6f80..4129d35adfb9d 100644
--- a/libc/hdr/types/CMakeLists.txt
+++ b/libc/hdr/types/CMakeLists.txt
@@ -170,6 +170,15 @@ add_proxy_header_library(
     libc.include.fcntl
 )
 
+add_proxy_header_library(
+  constraint_handler_t
+  HDRS
+    constraint_handler_t.h
+  FULL_BUILD_DEPENDS
+    libc.include.llvm-libc-types.constraint_handler_t
+    libc.include.stdlib
+)
+
 add_proxy_header_library(
   errno_t
   HDRS
diff --git a/libc/hdr/types/constraint_handler_t.h b/libc/hdr/types/constraint_handler_t.h
new file mode 100644
index 0000000000000..ca7798b84228e
--- /dev/null
+++ b/libc/hdr/types/constraint_handler_t.h
@@ -0,0 +1,18 @@
+//===-- Proxy for constraint_handler_t ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_TYPES_CONSTRAINT_HANDLER_T_H
+#define LLVM_LIBC_HDR_TYPES_CONSTRAINT_HANDLER_T_H
+
+#define LIBC_HAS_ANNEX_K
+
+#include "include/llvm-libc-types/constraint_handler_t.h"
+
+#undef LIBC_HAS_ANNEX_K
+
+#endif // LLVM_LIBC_HDR_TYPES_CONSTRAINT_HANDLER_T_H
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index 8e22baa8dfba1..fa9768a0066c5 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -299,3 +299,5 @@ add_header(EFI_SYSTEM_TABLE
 )
 
 add_header(errno_t HDR errno_t.h)
+
+add_header(constraint_handler_t HDR constraint_handler_t.h DEPENDS .errno_t)
diff --git a/libc/include/llvm-libc-types/constraint_handler_t.h b/libc/include/llvm-libc-types/constraint_handler_t.h
new file mode 100644
index 0000000000000..efd21296cd399
--- /dev/null
+++ b/libc/include/llvm-libc-types/constraint_handler_t.h
@@ -0,0 +1,21 @@
+//===-- Definition of type constraint_handler_t ---------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_INCLUDE_LLVM_LIBC_TYPES_CONSTRAINT_HANDLER_T_H
+#define LLVM_LIBC_INCLUDE_LLVM_LIBC_TYPES_CONSTRAINT_HANDLER_T_H
+
+#include "errno_t.h"
+
+#ifdef LIBC_HAS_ANNEX_K
+
+typedef void (*constraint_handler_t)(const char *__restrict, void *__restrict,
+                                     errno_t);
+
+#endif // LIBC_HAS_ANNEX_K
+
+#endif // LLVM_LIBC_INCLUDE_LLVM_LIBC_TYPES_CONSTRAINT_HANDLER_T_H
diff --git a/libc/include/stdlib.yaml b/libc/include/stdlib.yaml
index 3b2ff13c684b1..29fd6bc3a1e75 100644
--- a/libc/include/stdlib.yaml
+++ b/libc/include/stdlib.yaml
@@ -12,6 +12,7 @@ types:
   - type_name: __qsortcompare_t
   - type_name: __qsortrcompare_t
   - type_name: __search_compare_t
+  - type_name: constraint_handler_t
   - type_name: div_t
   - type_name: ldiv_t
   - type_name: lldiv_t