diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -85,15 +85,6 @@
     libc.src.errno.errno
 )
 
-add_object_library(
-  fork_callbacks
-  SRCS
-    fork_callbacks.cpp
-  HDRS
-    fork_callbacks.h
-  DEPENDS
-    .threads.mutex
-)
 
 add_header_library(
   integer_operations
diff --git a/libc/src/__support/threads/CMakeLists.txt b/libc/src/__support/threads/CMakeLists.txt
--- a/libc/src/__support/threads/CMakeLists.txt
+++ b/libc/src/__support/threads/CMakeLists.txt
@@ -16,6 +16,16 @@
     DEPENDS
       .${LIBC_TARGET_OS}.mutex
   )
+
+  add_object_library(
+    fork_callbacks
+    SRCS
+      fork_callbacks.cpp
+    HDRS
+      fork_callbacks.h
+    DEPENDS
+      .mutex
+  )
 endif()
 
 add_header_library(
diff --git a/libc/src/__support/fork_callbacks.h b/libc/src/__support/threads/fork_callbacks.h
rename from libc/src/__support/fork_callbacks.h
rename to libc/src/__support/threads/fork_callbacks.h
--- a/libc/src/__support/fork_callbacks.h
+++ b/libc/src/__support/threads/fork_callbacks.h
@@ -6,6 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#ifndef LLVM_LIBC_SRC_SUPPORT_THREAD_FORK_CALLBACKS_H
+#define LLVM_LIBC_SRC_SUPPORT_THREAD_FORK_CALLBACKS_H
+
 namespace __llvm_libc {
 
 using ForkCallback = void(void);
@@ -17,3 +20,5 @@
 void invoke_child_callbacks();
 
 } // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_SUPPORT_THREAD_FORK_CALLBACKS_H
diff --git a/libc/src/__support/fork_callbacks.cpp b/libc/src/__support/threads/fork_callbacks.cpp
rename from libc/src/__support/fork_callbacks.cpp
rename to libc/src/__support/threads/fork_callbacks.cpp
diff --git a/libc/src/pthread/CMakeLists.txt b/libc/src/pthread/CMakeLists.txt
--- a/libc/src/pthread/CMakeLists.txt
+++ b/libc/src/pthread/CMakeLists.txt
@@ -407,5 +407,5 @@
   DEPENDS
     libc.include.errno
     libc.include.pthread
-    libc.src.__support.fork_callbacks
+    libc.src.__support.threads.fork_callbacks
 )
diff --git a/libc/src/pthread/pthread_atfork.cpp b/libc/src/pthread/pthread_atfork.cpp
--- a/libc/src/pthread/pthread_atfork.cpp
+++ b/libc/src/pthread/pthread_atfork.cpp
@@ -9,7 +9,7 @@
 #include "pthread_atfork.h"
 
 #include "src/__support/common.h"
-#include "src/__support/fork_callbacks.h"
+#include "src/__support/threads/fork_callbacks.h"
 
 #include <errno.h>
 #include <pthread.h> // For pthread_* type definitions.
diff --git a/libc/src/unistd/linux/CMakeLists.txt b/libc/src/unistd/linux/CMakeLists.txt
--- a/libc/src/unistd/linux/CMakeLists.txt
+++ b/libc/src/unistd/linux/CMakeLists.txt
@@ -100,7 +100,7 @@
     libc.include.errno
     libc.include.unistd
     libc.include.sys_syscall
-    libc.src.__support.fork_callbacks
+    libc.src.__support.threads.fork_callbacks
     libc.src.__support.OSUtil.osutil
     libc.src.__support.threads.thread
     libc.src.errno.errno
diff --git a/libc/src/unistd/linux/fork.cpp b/libc/src/unistd/linux/fork.cpp
--- a/libc/src/unistd/linux/fork.cpp
+++ b/libc/src/unistd/linux/fork.cpp
@@ -10,7 +10,7 @@
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
 #include "src/__support/common.h"
-#include "src/__support/fork_callbacks.h"
+#include "src/__support/threads/fork_callbacks.h"
 #include "src/__support/threads/thread.h" // For thread self object
 
 #include <errno.h>