diff --git a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
index 9fc10375a1d379..e3dfe1a1529691 100644
--- a/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
+++ b/libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
@@ -71,6 +71,10 @@ function(_get_compile_options_from_config output_var)
     list(APPEND config_options "-DLIBC_QSORT_IMPL=${LIBC_CONF_QSORT_IMPL}")
   endif()
 
+  if(LIBC_TYPES_TIME_T_IS_32_BIT AND LLVM_LIBC_FULL_BUILD)
+    list(APPEND config_options "-DLIBC_TYPES_TIME_T_IS_32_BIT")
+  endif()
+
   set(${output_var} ${config_options} PARENT_SCOPE)
 endfunction(_get_compile_options_from_config)
 
diff --git a/libc/cmake/modules/LLVMLibCFlagRules.cmake b/libc/cmake/modules/LLVMLibCFlagRules.cmake
index 3629a7f111a7c5..69f31ace80dd3d 100644
--- a/libc/cmake/modules/LLVMLibCFlagRules.cmake
+++ b/libc/cmake/modules/LLVMLibCFlagRules.cmake
@@ -286,3 +286,16 @@ if(NOT((LIBC_TARGET_ARCHITECTURE_IS_X86 AND (LIBC_CPU_FEATURES MATCHES "SSE4_2")
        LIBC_TARGET_ARCHITECTURE_IS_AARCH64 OR LIBC_TARGET_OS_IS_GPU))
   set(SKIP_FLAG_EXPANSION_ROUND_OPT TRUE)
 endif()
+
+# Choose whether time_t is 32- or 64-bit, based on target architecture
+# and config options. This will be used to set a #define during the
+# library build, and also to select the right version of time_t.h for
+# the output headers.
+if(LIBC_TARGET_ARCHITECTURE_IS_ARM AND NOT (LIBC_CONF_TIME_64BIT))
+  # Set time_t to 32 bit for compatibility with glibc, unless
+  # configuration says otherwise
+  set(LIBC_TYPES_TIME_T_IS_32_BIT TRUE)
+else()
+  # Other platforms default to 64-bit time_t
+  set(LIBC_TYPES_TIME_T_IS_32_BIT FALSE)
+endif()
diff --git a/libc/cmake/modules/LLVMLibCHeaderRules.cmake b/libc/cmake/modules/LLVMLibCHeaderRules.cmake
index 3049f4db7301f6..c2c675bda26d31 100644
--- a/libc/cmake/modules/LLVMLibCHeaderRules.cmake
+++ b/libc/cmake/modules/LLVMLibCHeaderRules.cmake
@@ -9,8 +9,8 @@
 function(add_header target_name)
   cmake_parse_arguments(
     "ADD_HEADER"
-    ""    # No optional arguments
-    "HDR" # Single value arguments
+    ""             # No optional arguments
+    "HDR;DEST_HDR" # Single value arguments
     "DEPENDS"
     ${ARGN}
   )
@@ -18,7 +18,12 @@ function(add_header target_name)
     message(FATAL_ERROR "'add_header' rules requires the HDR argument specifying a headef file.")
   endif()
 
-  set(absolute_path ${CMAKE_CURRENT_SOURCE_DIR}/${ADD_HEADER_HDR})
+  if(ADD_HEADER_DEST_HDR)
+    set(dest_leaf_filename ${ADD_HEADER_DEST_HDR})
+  else()
+    set(dest_leaf_filename ${ADD_HEADER_HDR})
+  endif()
+  set(absolute_path ${CMAKE_CURRENT_SOURCE_DIR}/${dest_leaf_filename})
   file(RELATIVE_PATH relative_path ${LIBC_INCLUDE_SOURCE_DIR} ${absolute_path})
   set(dest_file ${LIBC_INCLUDE_DIR}/${relative_path})
   set(src_file ${CMAKE_CURRENT_SOURCE_DIR}/${ADD_HEADER_HDR})
diff --git a/libc/config/config.json b/libc/config/config.json
index 538fea53cc704a..2e72c0a3fd1d69 100644
--- a/libc/config/config.json
+++ b/libc/config/config.json
@@ -88,5 +88,11 @@
       "value": true,
       "doc": "Make setjmp save the value of x18, and longjmp restore it. The AArch64 ABI delegates this register to platform ABIs, which can choose whether to make it caller-saved."
     }
+  },
+  "time": {
+    "LIBC_CONF_TIME_64BIT": {
+      "value": false,
+      "doc": "Force the size of time_t to 64 bits, even on platforms where compatibility considerations would otherwise make it 32-bit."
+    }
   }
 }
diff --git a/libc/docs/configure.rst b/libc/docs/configure.rst
index 950de0eee4c05d..54ca5d55d7b243 100644
--- a/libc/docs/configure.rst
+++ b/libc/docs/configure.rst
@@ -52,3 +52,5 @@ to learn about the defaults for your platform and target.
 * **"string" options**
     - ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.
     - ``LIBC_CONF_STRING_UNSAFE_WIDE_READ``: Read more than a byte at a time to perform byte-string operations like strlen.
+* **"time" options**
+    - ``LIBC_CONF_TIME_64BIT``: Force the size of time_t to 64 bits, even on platforms where compatibility considerations would otherwise make it 32-bit.
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index 9e77ab226ce6c2..0fa86e0152f9ba 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -59,7 +59,11 @@ add_header(pthread_rwlockattr_t HDR pthread_rwlockattr_t.h)
 add_header(pthread_spinlock_t HDR pthread_spinlock_t.h DEPENDS .pid_t)
 add_header(pthread_t HDR pthread_t.h DEPENDS .__thread_type)
 add_header(rlim_t HDR rlim_t.h)
-add_header(time_t HDR time_t.h)
+if(LIBC_TYPES_TIME_T_IS_32_BIT)
+  add_header(time_t HDR time_t_32.h DEST_HDR time_t.h)
+else()
+  add_header(time_t HDR time_t_64.h DEST_HDR time_t.h)
+endif()
 add_header(stack_t HDR stack_t.h DEPENDS .size_t)
 add_header(suseconds_t HDR suseconds_t.h)
 add_header(struct_flock HDR struct_flock.h DEPENDS .off_t .pid_t)
diff --git a/libc/include/llvm-libc-types/time_t.h b/libc/include/llvm-libc-types/time_t.h
index 59953b343ba963..76920dc07ec69c 100644
--- a/libc/include/llvm-libc-types/time_t.h
+++ b/libc/include/llvm-libc-types/time_t.h
@@ -1,4 +1,4 @@
-//===-- Definition of the type time_t -------------------------------------===//
+//===-- Definition of the type time_t, for use during the libc build ------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -9,10 +9,10 @@
 #ifndef LLVM_LIBC_TYPES_TIME_T_H
 #define LLVM_LIBC_TYPES_TIME_T_H
 
-#if (defined(__arm__) || defined(_M_ARM))
-typedef __INTPTR_TYPE__ time_t;
+#ifdef LIBC_TYPES_TIME_T_IS_32_BIT
+#include "time_t_32.h"
 #else
-typedef __INT64_TYPE__ time_t;
+#include "time_t_64.h"
 #endif
 
 #endif // LLVM_LIBC_TYPES_TIME_T_H
diff --git a/libc/include/llvm-libc-types/time_t_32.h b/libc/include/llvm-libc-types/time_t_32.h
new file mode 100644
index 00000000000000..2c415f6fa9dcab
--- /dev/null
+++ b/libc/include/llvm-libc-types/time_t_32.h
@@ -0,0 +1,14 @@
+//===-- Definition of the type time_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_TYPES_TIME_T_32_H
+#define LLVM_LIBC_TYPES_TIME_T_32_H
+
+typedef __INT32_TYPE__ time_t;
+
+#endif // LLVM_LIBC_TYPES_TIME_T_32_H
diff --git a/libc/include/llvm-libc-types/time_t_64.h b/libc/include/llvm-libc-types/time_t_64.h
new file mode 100644
index 00000000000000..8f7fd3233646e6
--- /dev/null
+++ b/libc/include/llvm-libc-types/time_t_64.h
@@ -0,0 +1,14 @@
+//===-- Definition of the type time_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_TYPES_TIME_T_64_H
+#define LLVM_LIBC_TYPES_TIME_T_64_H
+
+typedef __INT64_TYPE__ time_t;
+
+#endif // LLVM_LIBC_TYPES_TIME_T_64_H